











Network Working Group                                 P. Resnick, Editor

Request for Comments: 2822                         QUALCOMM Incorporated

Obsoletes: 822                                                April 2001

Category: Standards Track





                        Internet Message Format



Status of this Memo



   This document specifies an Internet standards track protocol for the

   Internet community, and requests discussion and suggestions for

   improvements.  Please refer to the current edition of the "Internet

   Official Protocol Standards" (STD 1) for the standardization state

   and status of this protocol.  Distribution of this memo is unlimited.



Copyright Notice



   Copyright (C) The Internet Society (2001).  All Rights Reserved.



Abstract



   This standard specifies a syntax for text messages that are sent

   between computer users, within the framework of "electronic mail"

   messages.  This standard supersedes the one specified in Request For

   Comments (RFC) 822, "Standard for the Format of ARPA Internet Text

   Messages", updating it to reflect current practice and incorporating

   incremental changes that were specified in other RFCs.



Table of Contents



   1. Introduction ............................................... 3

   1.1. Scope .................................................... 3

   1.2. Notational conventions ................................... 4

   1.2.1. Requirements notation .................................. 4

   1.2.2. Syntactic notation ..................................... 4

   1.3. Structure of this document ............................... 4

   2. Lexical Analysis of Messages ............................... 5

   2.1. General Description ...................................... 5

   2.1.1. Line Length Limits ..................................... 6

   2.2. Header Fields ............................................ 7

   2.2.1. Unstructured Header Field Bodies ....................... 7

   2.2.2. Structured Header Field Bodies ......................... 7

   2.2.3. Long Header Fields ..................................... 7

   2.3. Body ..................................................... 8

   3. Syntax ..................................................... 9

   3.1. Introduction ............................................. 9

   3.2. Lexical Tokens ........................................... 9







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   3.2.1. Primitive Tokens ....................................... 9

   3.2.2. Quoted characters ......................................10

   3.2.3. Folding white space and comments .......................11

   3.2.4. Atom ...................................................12

   3.2.5. Quoted strings .........................................13

   3.2.6. Miscellaneous tokens ...................................13

   3.3. Date and Time Specification ..............................14

   3.4. Address Specification ....................................15

   3.4.1. Addr-spec specification ................................16

   3.5 Overall message syntax ....................................17

   3.6. Field definitions ........................................18

   3.6.1. The origination date field .............................20

   3.6.2. Originator fields ......................................21

   3.6.3. Destination address fields .............................22

   3.6.4. Identification fields ..................................23

   3.6.5. Informational fields ...................................26

   3.6.6. Resent fields ..........................................26

   3.6.7. Trace fields ...........................................28

   3.6.8. Optional fields ........................................29

   4. Obsolete Syntax ............................................29

   4.1. Miscellaneous obsolete tokens ............................30

   4.2. Obsolete folding white space .............................31

   4.3. Obsolete Date and Time ...................................31

   4.4. Obsolete Addressing ......................................33

   4.5. Obsolete header fields ...................................33

   4.5.1. Obsolete origination date field ........................34

   4.5.2. Obsolete originator fields .............................34

   4.5.3. Obsolete destination address fields ....................34

   4.5.4. Obsolete identification fields .........................35

   4.5.5. Obsolete informational fields ..........................35

   4.5.6. Obsolete resent fields .................................35

   4.5.7. Obsolete trace fields ..................................36

   4.5.8. Obsolete optional fields ...............................36

   5. Security Considerations ....................................36

   6. Bibliography ...............................................37

   7. Editor's Address ...........................................38

   8. Acknowledgements ...........................................39

   Appendix A. Example messages ..................................41

   A.1. Addressing examples ......................................41

   A.1.1. A message from one person to another with simple

          addressing .............................................41

   A.1.2. Different types of mailboxes ...........................42

   A.1.3. Group addresses ........................................43

   A.2. Reply messages ...........................................43

   A.3. Resent messages ..........................................44

   A.4. Messages with trace fields ...............................46

   A.5. White space, comments, and other oddities ................47

   A.6. Obsoleted forms ..........................................47







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   A.6.1. Obsolete addressing ....................................48

   A.6.2. Obsolete dates .........................................48

   A.6.3. Obsolete white space and comments ......................48

   Appendix B. Differences from earlier standards ................49

   Appendix C. Notices ...........................................50

   Full Copyright Statement ......................................51



1. Introduction



1.1. Scope



   This standard specifies a syntax for text messages that are sent

   between computer users, within the framework of "electronic mail"

   messages.  This standard supersedes the one specified in Request For

   Comments (RFC) 822, "Standard for the Format of ARPA Internet Text

   Messages" [RFC822], updating it to reflect current practice and

   incorporating incremental changes that were specified in other RFCs

   [STD3].



   This standard specifies a syntax only for text messages.  In

   particular, it makes no provision for the transmission of images,

   audio, or other sorts of structured data in electronic mail messages.

   There are several extensions published, such as the MIME document

   series [RFC2045, RFC2046, RFC2049], which describe mechanisms for the

   transmission of such data through electronic mail, either by

   extending the syntax provided here or by structuring such messages to

   conform to this syntax.  Those mechanisms are outside of the scope of

   this standard.



   In the context of electronic mail, messages are viewed as having an

   envelope and contents.  The envelope contains whatever information is

   needed to accomplish transmission and delivery.  (See [RFC2821] for a

   discussion of the envelope.)  The contents comprise the object to be

   delivered to the recipient.  This standard applies only to the format

   and some of the semantics of message contents.  It contains no

   specification of the information in the envelope.



   However, some message systems may use information from the contents

   to create the envelope.  It is intended that this standard facilitate

   the acquisition of such information by programs.



   This specification is intended as a definition of what message

   content format is to be passed between systems.  Though some message

   systems locally store messages in this format (which eliminates the

   need for translation between formats) and others use formats that

   differ from the one specified in this standard, local storage is

   outside of the scope of this standard.









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   Note: This standard is not intended to dictate the internal formats

   used by sites, the specific message system features that they are

   expected to support, or any of the characteristics of user interface

   programs that create or read messages.  In addition, this standard

   does not specify an encoding of the characters for either transport

   or storage; that is, it does not specify the number of bits used or

   how those bits are specifically transferred over the wire or stored

   on disk.



1.2. Notational conventions



1.2.1. Requirements notation



   This document occasionally uses terms that appear in capital letters.

   When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD

   NOT", and "MAY" appear capitalized, they are being used to indicate

   particular requirements of this specification.  A discussion of the

   meanings of these terms appears in [RFC2119].



1.2.2. Syntactic notation



   This standard uses the Augmented Backus-Naur Form (ABNF) notation

   specified in [RFC2234] for the formal definitions of the syntax of

   messages.  Characters will be specified either by a decimal value

   (e.g., the value %d65 for uppercase A and %d97 for lowercase A) or by

   a case-insensitive literal value enclosed in quotation marks (e.g.,

   "A" for either uppercase or lowercase A).  See [RFC2234] for the full

   description of the notation.



1.3. Structure of this document



   This document is divided into several sections.



   This section, section 1, is a short introduction to the document.



   Section 2 lays out the general description of a message and its

   constituent parts.  This is an overview to help the reader understand

   some of the general principles used in the later portions of this

   document.  Any examples in this section MUST NOT be taken as

   specification of the formal syntax of any part of a message.



   Section 3 specifies formal ABNF rules for the structure of each part

   of a message (the syntax) and describes the relationship between

   those parts and their meaning in the context of a message (the

   semantics).  That is, it describes the actual rules for the structure

   of each part of a message (the syntax) as well as a description of

   the parts and instructions on how they ought to be interpreted (the

   semantics).  This includes analysis of the syntax and semantics of







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   subparts of messages that have specific structure.  The syntax

   included in section 3 represents messages as they MUST be created.

   There are also notes in section 3 to indicate if any of the options

   specified in the syntax SHOULD be used over any of the others.



   Both sections 2 and 3 describe messages that are legal to generate

   for purposes of this standard.



   Section 4 of this document specifies an "obsolete" syntax.  There are

   references in section 3 to these obsolete syntactic elements.  The

   rules of the obsolete syntax are elements that have appeared in

   earlier revisions of this standard or have previously been widely

   used in Internet messages.  As such, these elements MUST be

   interpreted by parsers of messages in order to be conformant to this

   standard.  However, since items in this syntax have been determined

   to be non-interoperable or to cause significant problems for

   recipients of messages, they MUST NOT be generated by creators of

   conformant messages.



   Section 5 details security considerations to take into account when

   implementing this standard.



   Section 6 is a bibliography of references in this document.



   Section 7 contains the editor's address.



   Section 8 contains acknowledgements.



   Appendix A lists examples of different sorts of messages.  These

   examples are not exhaustive of the types of messages that appear on

   the Internet, but give a broad overview of certain syntactic forms.



   Appendix B lists the differences between this standard and earlier

   standards for Internet messages.



   Appendix C has copyright and intellectual property notices.



2. Lexical Analysis of Messages



2.1. General Description



   At the most basic level, a message is a series of characters.  A

   message that is conformant with this standard is comprised of

   characters with values in the range 1 through 127 and interpreted as

   US-ASCII characters [ASCII].  For brevity, this document sometimes

   refers to this range of characters as simply "US-ASCII characters".











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   Note: This standard specifies that messages are made up of characters

   in the US-ASCII range of 1 through 127.  There are other documents,

   specifically the MIME document series [RFC2045, RFC2046, RFC2047,

   RFC2048, RFC2049], that extend this standard to allow for values

   outside of that range.  Discussion of those mechanisms is not within

   the scope of this standard.



   Messages are divided into lines of characters.  A line is a series of

   characters that is delimited with the two characters carriage-return

   and line-feed; that is, the carriage return (CR) character (ASCII

   value 13) followed immediately by the line feed (LF) character (ASCII

   value 10).  (The carriage-return/line-feed pair is usually written in

   this document as "CRLF".)



   A message consists of header fields (collectively called "the header

   of the message") followed, optionally, by a body.  The header is a

   sequence of lines of characters with special syntax as defined in

   this standard. The body is simply a sequence of characters that

   follows the header and is separated from the header by an empty line

   (i.e., a line with nothing preceding the CRLF).



2.1.1. Line Length Limits



   There are two limits that this standard places on the number of

   characters in a line. Each line of characters MUST be no more than

   998 characters, and SHOULD be no more than 78 characters, excluding

   the CRLF.



   The 998 character limit is due to limitations in many implementations

   which send, receive, or store Internet Message Format messages that

   simply cannot handle more than 998 characters on a line. Receiving

   implementations would do well to handle an arbitrarily large number

   of characters in a line for robustness sake. However, there are so

   many implementations which (in compliance with the transport

   requirements of [RFC2821]) do not accept messages containing more

   than 1000 character including the CR and LF per line, it is important

   for implementations not to create such messages.



   The more conservative 78 character recommendation is to accommodate

   the many implementations of user interfaces that display these

   messages which may truncate, or disastrously wrap, the display of

   more than 78 characters per line, in spite of the fact that such

   implementations are non-conformant to the intent of this

   specification (and that of [RFC2821] if they actually cause

   information to be lost). Again, even though this limitation is put on

   messages, it is encumbant upon implementations which display messages











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   to handle an arbitrarily large number of characters in a line

   (certainly at least up to the 998 character limit) for the sake of

   robustness.



2.2. Header Fields



   Header fields are lines composed of a field name, followed by a colon

   (":"), followed by a field body, and terminated by CRLF.  A field

   name MUST be composed of printable US-ASCII characters (i.e.,

   characters that have values between 33 and 126, inclusive), except

   colon.  A field body may be composed of any US-ASCII characters,

   except for CR and LF.  However, a field body may contain CRLF when

   used in header "folding" and  "unfolding" as described in section

   2.2.3.  All field bodies MUST conform to the syntax described in

   sections 3 and 4 of this standard.



2.2.1. Unstructured Header Field Bodies



   Some field bodies in this standard are defined simply as

   "unstructured" (which is specified below as any US-ASCII characters,

   except for CR and LF) with no further restrictions.  These are

   referred to as unstructured field bodies.  Semantically, unstructured

   field bodies are simply to be treated as a single line of characters

   with no further processing (except for header "folding" and

   "unfolding" as described in section 2.2.3).



2.2.2. Structured Header Field Bodies



   Some field bodies in this standard have specific syntactical

   structure more restrictive than the unstructured field bodies

   described above. These are referred to as "structured" field bodies.

   Structured field bodies are sequences of specific lexical tokens as

   described in sections 3 and 4 of this standard.  Many of these tokens

   are allowed (according to their syntax) to be introduced or end with

   comments (as described in section 3.2.3) as well as the space (SP,

   ASCII value 32) and horizontal tab (HTAB, ASCII value 9) characters

   (together known as the white space characters, WSP), and those WSP

   characters are subject to header "folding" and "unfolding" as

   described in section 2.2.3.  Semantic analysis of structured field

   bodies is given along with their syntax.



2.2.3. Long Header Fields



   Each header field is logically a single line of characters comprising

   the field name, the colon, and the field body.  For convenience

   however, and to deal with the 998/78 character limitations per line,

   the field body portion of a header field can be split into a multiple

   line representation; this is called "folding".  The general rule is







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   that wherever this standard allows for folding white space (not

   simply WSP characters), a CRLF may be inserted before any WSP.  For

   example, the header field:



           Subject: This is a test



   can be represented as:



           Subject: This

            is a test



   Note: Though structured field bodies are defined in such a way that

   folding can take place between many of the lexical tokens (and even

   within some of the lexical tokens), folding SHOULD be limited to

   placing the CRLF at higher-level syntactic breaks.  For instance, if

   a field body is defined as comma-separated values, it is recommended

   that folding occur after the comma separating the structured items in

   preference to other places where the field could be folded, even if

   it is allowed elsewhere.



   The process of moving from this folded multiple-line representation

   of a header field to its single line representation is called

   "unfolding". Unfolding is accomplished by simply removing any CRLF

   that is immediately followed by WSP.  Each header field should be

   treated in its unfolded form for further syntactic and semantic

   evaluation.



2.3. Body



   The body of a message is simply lines of US-ASCII characters.  The

   only two limitations on the body are as follows:



   - CR and LF MUST only occur together as CRLF; they MUST NOT appear

     independently in the body.



   - Lines of characters in the body MUST be limited to 998 characters,

     and SHOULD be limited to 78 characters, excluding the CRLF.



   Note: As was stated earlier, there are other standards documents,

   specifically the MIME documents [RFC2045, RFC2046, RFC2048, RFC2049]

   that extend this standard to allow for different sorts of message

   bodies.  Again, these mechanisms are beyond the scope of this

   document.

















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3. Syntax



3.1. Introduction



   The syntax as given in this section defines the legal syntax of

   Internet messages.  Messages that are conformant to this standard

   MUST conform to the syntax in this section.  If there are options in

   this section where one option SHOULD be generated, that is indicated

   either in the prose or in a comment next to the syntax.



   For the defined expressions, a short description of the syntax and

   use is given, followed by the syntax in ABNF, followed by a semantic

   analysis.  Primitive tokens that are used but otherwise unspecified

   come from [RFC2234].



   In some of the definitions, there will be nonterminals whose names

   start with "obs-".  These "obs-" elements refer to tokens defined in

   the obsolete syntax in section 4.  In all cases, these productions

   are to be ignored for the purposes of generating legal Internet

   messages and MUST NOT be used as part of such a message.  However,

   when interpreting messages, these tokens MUST be honored as part of

   the legal syntax.  In this sense, section 3 defines a grammar for

   generation of messages, with "obs-" elements that are to be ignored,

   while section 4 adds grammar for interpretation of messages.



3.2. Lexical Tokens



   The following rules are used to define an underlying lexical

   analyzer, which feeds tokens to the higher-level parsers.  This

   section defines the tokens used in structured header field bodies.



   Note: Readers of this standard need to pay special attention to how

   these lexical tokens are used in both the lower-level and

   higher-level syntax later in the document.  Particularly, the white

   space tokens and the comment tokens defined in section 3.2.3 get used

   in the lower-level tokens defined here, and those lower-level tokens

   are in turn used as parts of the higher-level tokens defined later.

   Therefore, the white space and comments may be allowed in the

   higher-level tokens even though they may not explicitly appear in a

   particular definition.



3.2.1. Primitive Tokens



   The following are primitive tokens referred to elsewhere in this

   standard, but not otherwise defined in [RFC2234].  Some of them will

   not appear anywhere else in the syntax, but they are convenient to

   refer to in other parts of this document.









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   Note: The "specials" below are just such an example.  Though the

   specials token does not appear anywhere else in this standard, it is

   useful for implementers who use tools that lexically analyze

   messages.  Each of the characters in specials can be used to indicate

   a tokenization point in lexical analysis.



NO-WS-CTL       =       %d1-8 /         ; US-ASCII control characters

                        %d11 /          ;  that do not include the

                        %d12 /          ;  carriage return, line feed,

                        %d14-31 /       ;  and white space characters

                        %d127



text            =       %d1-9 /         ; Characters excluding CR and LF

                        %d11 /

                        %d12 /

                        %d14-127 /

                        obs-text



specials        =       "(" / ")" /     ; Special characters used in

                        "<" / ">" /     ;  other parts of the syntax

                        "[" / "]" /

                        ":" / ";" /

                        "@" / "\" /

                        "," / "." /

                        DQUOTE



   No special semantics are attached to these tokens.  They are simply

   single characters.



3.2.2. Quoted characters



   Some characters are reserved for special interpretation, such as

   delimiting lexical tokens.  To permit use of these characters as

   uninterpreted data, a quoting mechanism is provided.



quoted-pair     =       ("\" text) / obs-qp



   Where any quoted-pair appears, it is to be interpreted as the text

   character alone.  That is to say, the "\" character that appears as

   part of a quoted-pair is semantically "invisible".



   Note: The "\" character may appear in a message where it is not part

   of a quoted-pair.  A "\" character that does not appear in a

   quoted-pair is not semantically invisible.  The only places in this

   standard where quoted-pair currently appears are ccontent, qcontent,

   dcontent, no-fold-quote, and no-fold-literal.











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3.2.3. Folding white space and comments



   White space characters, including white space used in folding

   (described in section 2.2.3), may appear between many elements in

   header field bodies.  Also, strings of characters that are treated as

   comments may be included in structured field bodies as characters

   enclosed in parentheses.  The following defines the folding white

   space (FWS) and comment constructs.



   Strings of characters enclosed in parentheses are considered comments

   so long as they do not appear within a "quoted-string", as defined in

   section 3.2.5.  Comments may nest.



   There are several places in this standard where comments and FWS may

   be freely inserted.  To accommodate that syntax, an additional token

   for "CFWS" is defined for places where comments and/or FWS can occur.

   However, where CFWS occurs in this standard, it MUST NOT be inserted

   in such a way that any line of a folded header field is made up

   entirely of WSP characters and nothing else.



FWS             =       ([*WSP CRLF] 1*WSP) /   ; Folding white space

                        obs-FWS



ctext           =       NO-WS-CTL /     ; Non white space controls



                        %d33-39 /       ; The rest of the US-ASCII

                        %d42-91 /       ;  characters not including "(",

                        %d93-126        ;  ")", or "\"



ccontent        =       ctext / quoted-pair / comment



comment         =       "(" *([FWS] ccontent) [FWS] ")"



CFWS            =       *([FWS] comment) (([FWS] comment) / FWS)



   Throughout this standard, where FWS (the folding white space token)

   appears, it indicates a place where header folding, as discussed in

   section 2.2.3, may take place.  Wherever header folding appears in a

   message (that is, a header field body containing a CRLF followed by

   any WSP), header unfolding (removal of the CRLF) is performed before

   any further lexical analysis is performed on that header field

   according to this standard.  That is to say, any CRLF that appears in

   FWS is semantically "invisible."



   A comment is normally used in a structured field body to provide some

   human readable informational text.  Since a comment is allowed to

   contain FWS, folding is permitted within the comment.  Also note that

   since quoted-pair is allowed in a comment, the parentheses and







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   backslash characters may appear in a comment so long as they appear

   as a quoted-pair.  Semantically, the enclosing parentheses are not

   part of the comment; the comment is what is contained between the two

   parentheses.  As stated earlier, the "\" in any quoted-pair and the

   CRLF in any FWS that appears within the comment are semantically

   "invisible" and therefore not part of the comment either.



   Runs of FWS, comment or CFWS that occur between lexical tokens in a

   structured field header are semantically interpreted as a single

   space character.



3.2.4. Atom



   Several productions in structured header field bodies are simply

   strings of certain basic characters.  Such productions are called

   atoms.



   Some of the structured header field bodies also allow the period

   character (".", ASCII value 46) within runs of atext.  An additional

   "dot-atom" token is defined for those purposes.



atext           =       ALPHA / DIGIT / ; Any character except controls,

                        "!" / "#" /     ;  SP, and specials.

                        "$" / "%" /     ;  Used for atoms

                        "&" / "'" /

                        "*" / "+" /

                        "-" / "/" /

                        "=" / "?" /

                        "^" / "_" /

                        "`" / "{" /

                        "|" / "}" /

                        "~"



atom            =       [CFWS] 1*atext [CFWS]



dot-atom        =       [CFWS] dot-atom-text [CFWS]



dot-atom-text   =       1*atext *("." 1*atext)



   Both atom and dot-atom are interpreted as a single unit, comprised of

   the string of characters that make it up.  Semantically, the optional

   comments and FWS surrounding the rest of the characters are not part

   of the atom; the atom is only the run of atext characters in an atom,

   or the atext and "." characters in a dot-atom.















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3.2.5. Quoted strings



   Strings of characters that include characters other than those

   allowed in atoms may be represented in a quoted string format, where

   the characters are surrounded by quote (DQUOTE, ASCII value 34)

   characters.



qtext           =       NO-WS-CTL /     ; Non white space controls



                        %d33 /          ; The rest of the US-ASCII

                        %d35-91 /       ;  characters not including "\"

                        %d93-126        ;  or the quote character



qcontent        =       qtext / quoted-pair



quoted-string   =       [CFWS]

                        DQUOTE *([FWS] qcontent) [FWS] DQUOTE

                        [CFWS]



   A quoted-string is treated as a unit.  That is, quoted-string is

   identical to atom, semantically.  Since a quoted-string is allowed to

   contain FWS, folding is permitted.  Also note that since quoted-pair

   is allowed in a quoted-string, the quote and backslash characters may

   appear in a quoted-string so long as they appear as a quoted-pair.



   Semantically, neither the optional CFWS outside of the quote

   characters nor the quote characters themselves are part of the

   quoted-string; the quoted-string is what is contained between the two

   quote characters.  As stated earlier, the "\" in any quoted-pair and

   the CRLF in any FWS/CFWS that appears within the quoted-string are

   semantically "invisible" and therefore not part of the quoted-string

   either.



3.2.6. Miscellaneous tokens



   Three additional tokens are defined, word and phrase for combinations

   of atoms and/or quoted-strings, and unstructured for use in

   unstructured header fields and in some places within structured

   header fields.



word            =       atom / quoted-string



phrase          =       1*word / obs-phrase

















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utext           =       NO-WS-CTL /     ; Non white space controls

                        %d33-126 /      ; The rest of US-ASCII

                        obs-utext



unstructured    =       *([FWS] utext) [FWS]



3.3. Date and Time Specification



   Date and time occur in several header fields.  This section specifies

   the syntax for a full date and time specification.  Though folding

   white space is permitted throughout the date-time specification, it

   is RECOMMENDED that a single space be used in each place that FWS

   appears (whether it is required or optional); some older

   implementations may not interpret other occurrences of folding white

   space correctly.



date-time       =       [ day-of-week "," ] date FWS time [CFWS]



day-of-week     =       ([FWS] day-name) / obs-day-of-week



day-name        =       "Mon" / "Tue" / "Wed" / "Thu" /

                        "Fri" / "Sat" / "Sun"



date            =       day month year



year            =       4*DIGIT / obs-year



month           =       (FWS month-name FWS) / obs-month



month-name      =       "Jan" / "Feb" / "Mar" / "Apr" /

                        "May" / "Jun" / "Jul" / "Aug" /

                        "Sep" / "Oct" / "Nov" / "Dec"



day             =       ([FWS] 1*2DIGIT) / obs-day



time            =       time-of-day FWS zone



time-of-day     =       hour ":" minute [ ":" second ]



hour            =       2DIGIT / obs-hour



minute          =       2DIGIT / obs-minute



second          =       2DIGIT / obs-second



zone            =       (( "+" / "-" ) 4DIGIT) / obs-zone











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   The day is the numeric day of the month.  The year is any numeric

   year 1900 or later.



   The time-of-day specifies the number of hours, minutes, and

   optionally seconds since midnight of the date indicated.



   The date and time-of-day SHOULD express local time.



   The zone specifies the offset from Coordinated Universal Time (UTC,

   formerly referred to as "Greenwich Mean Time") that the date and

   time-of-day represent.  The "+" or "-" indicates whether the

   time-of-day is ahead of (i.e., east of) or behind (i.e., west of)

   Universal Time.  The first two digits indicate the number of hours

   difference from Universal Time, and the last two digits indicate the

   number of minutes difference from Universal Time.  (Hence, +hhmm

   means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm)

   minutes).  The form "+0000" SHOULD be used to indicate a time zone at

   Universal Time.  Though "-0000" also indicates Universal Time, it is

   used to indicate that the time was generated on a system that may be

   in a local time zone other than Universal Time and therefore

   indicates that the date-time contains no information about the local

   time zone.



   A date-time specification MUST be semantically valid.  That is, the

   day-of-the-week (if included) MUST be the day implied by the date,

   the numeric day-of-month MUST be between 1 and the number of days

   allowed for the specified month (in the specified year), the

   time-of-day MUST be in the range 00:00:00 through 23:59:60 (the

   number of seconds allowing for a leap second; see [STD12]), and the

   zone MUST be within the range -9959 through +9959.



3.4. Address Specification



   Addresses occur in several message header fields to indicate senders

   and recipients of messages.  An address may either be an individual

   mailbox, or a group of mailboxes.



address         =       mailbox / group



mailbox         =       name-addr / addr-spec



name-addr       =       [display-name] angle-addr



angle-addr      =       [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr



group           =       display-name ":" [mailbox-list / CFWS] ";"

                        [CFWS]









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display-name    =       phrase



mailbox-list    =       (mailbox *("," mailbox)) / obs-mbox-list



address-list    =       (address *("," address)) / obs-addr-list



   A mailbox receives mail.  It is a conceptual entity which does not

   necessarily pertain to file storage.  For example, some sites may

   choose to print mail on a printer and deliver the output to the

   addressee's desk.  Normally, a mailbox is comprised of two parts: (1)

   an optional display name that indicates the name of the recipient

   (which could be a person or a system) that could be displayed to the

   user of a mail application, and (2) an addr-spec address enclosed in

   angle brackets ("<" and ">").  There is also an alternate simple form

   of a mailbox where the addr-spec address appears alone, without the

   recipient's name or the angle brackets.  The Internet addr-spec

   address is described in section 3.4.1.



   Note: Some legacy implementations used the simple form where the

   addr-spec appears without the angle brackets, but included the name

   of the recipient in parentheses as a comment following the addr-spec.

   Since the meaning of the information in a comment is unspecified,

   implementations SHOULD use the full name-addr form of the mailbox,

   instead of the legacy form, to specify the display name associated

   with a mailbox.  Also, because some legacy implementations interpret

   the comment, comments generally SHOULD NOT be used in address fields

   to avoid confusing such implementations.



   When it is desirable to treat several mailboxes as a single unit

   (i.e., in a distribution list), the group construct can be used.  The

   group construct allows the sender to indicate a named group of

   recipients. This is done by giving a display name for the group,

   followed by a colon, followed by a comma separated list of any number

   of mailboxes (including zero and one), and ending with a semicolon.

   Because the list of mailboxes can be empty, using the group construct

   is also a simple way to communicate to recipients that the message

   was sent to one or more named sets of recipients, without actually

   providing the individual mailbox address for each of those

   recipients.



3.4.1. Addr-spec specification



   An addr-spec is a specific Internet identifier that contains a

   locally interpreted string followed by the at-sign character ("@",

   ASCII value 64) followed by an Internet domain.  The locally

   interpreted string is either a quoted-string or a dot-atom.  If the

   string can be represented as a dot-atom (that is, it contains no

   characters other than atext characters or "." surrounded by atext







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   characters), then the dot-atom form SHOULD be used and the

   quoted-string form SHOULD NOT be used. Comments and folding white

   space SHOULD NOT be used around the "@" in the addr-spec.



addr-spec       =       local-part "@" domain



local-part      =       dot-atom / quoted-string / obs-local-part



domain          =       dot-atom / domain-literal / obs-domain



domain-literal  =       [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]



dcontent        =       dtext / quoted-pair



dtext           =       NO-WS-CTL /     ; Non white space controls



                        %d33-90 /       ; The rest of the US-ASCII

                        %d94-126        ;  characters not including "[",

                                        ;  "]", or "\"



   The domain portion identifies the point to which the mail is

   delivered. In the dot-atom form, this is interpreted as an Internet

   domain name (either a host name or a mail exchanger name) as

   described in [STD3, STD13, STD14].  In the domain-literal form, the

   domain is interpreted as the literal Internet address of the

   particular host.  In both cases, how addressing is used and how

   messages are transported to a particular host is covered in the mail

   transport document [RFC2821].  These mechanisms are outside of the

   scope of this document.



   The local-part portion is a domain dependent string.  In addresses,

   it is simply interpreted on the particular host as a name of a

   particular mailbox.



3.5 Overall message syntax



   A message consists of header fields, optionally followed by a message

   body.  Lines in a message MUST be a maximum of 998 characters

   excluding the CRLF, but it is RECOMMENDED that lines be limited to 78

   characters excluding the CRLF.  (See section 2.1.1 for explanation.)

   In a message body, though all of the characters listed in the text

   rule MAY be used, the use of US-ASCII control characters (values 1

   through 8, 11, 12, and 14 through 31) is discouraged since their

   interpretation by receivers for display is not guaranteed.















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message         =       (fields / obs-fields)

                        [CRLF body]



body            =       *(*998text CRLF) *998text



   The header fields carry most of the semantic information and are

   defined in section 3.6.  The body is simply a series of lines of text

   which are uninterpreted for the purposes of this standard.



3.6. Field definitions



   The header fields of a message are defined here.  All header fields

   have the same general syntactic structure: A field name, followed by

   a colon, followed by the field body.  The specific syntax for each

   header field is defined in the subsequent sections.



   Note: In the ABNF syntax for each field in subsequent sections, each

   field name is followed by the required colon.  However, for brevity

   sometimes the colon is not referred to in the textual description of

   the syntax.  It is, nonetheless, required.



   It is important to note that the header fields are not guaranteed to

   be in a particular order.  They may appear in any order, and they

   have been known to be reordered occasionally when transported over

   the Internet.  However, for the purposes of this standard, header

   fields SHOULD NOT be reordered when a message is transported or

   transformed.  More importantly, the trace header fields and resent

   header fields MUST NOT be reordered, and SHOULD be kept in blocks

   prepended to the message.  See sections 3.6.6 and 3.6.7 for more

   information.



   The only required header fields are the origination date field and

   the originator address field(s).  All other header fields are

   syntactically optional.  More information is contained in the table

   following this definition.



fields          =       *(trace

                          *(resent-date /

                           resent-from /

                           resent-sender /

                           resent-to /

                           resent-cc /

                           resent-bcc /

                           resent-msg-id))

                        *(orig-date /

                        from /

                        sender /

                        reply-to /







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                        to /

                        cc /

                        bcc /

                        message-id /

                        in-reply-to /

                        references /

                        subject /

                        comments /

                        keywords /

                        optional-field)



   The following table indicates limits on the number of times each

   field may occur in a message header as well as any special

   limitations on the use of those fields.  An asterisk next to a value

   in the minimum or maximum column indicates that a special restriction

   appears in the Notes column.



Field           Min number      Max number      Notes



trace           0               unlimited       Block prepended - see

                                                3.6.7



resent-date     0*              unlimited*      One per block, required

                                                if other resent fields

                                                present - see 3.6.6



resent-from     0               unlimited*      One per block - see

                                                3.6.6



resent-sender   0*              unlimited*      One per block, MUST

                                                occur with multi-address

                                                resent-from - see 3.6.6



resent-to       0               unlimited*      One per block - see

                                                3.6.6



resent-cc       0               unlimited*      One per block - see

                                                3.6.6



resent-bcc      0               unlimited*      One per block - see

                                                3.6.6



resent-msg-id   0               unlimited*      One per block - see

                                                3.6.6



orig-date       1               1



from            1               1               See sender and 3.6.2







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sender          0*              1               MUST occur with multi-

                                                address from - see 3.6.2



reply-to        0               1



to              0               1



cc              0               1



bcc             0               1



message-id      0*              1               SHOULD be present - see

                                                3.6.4



in-reply-to     0*              1               SHOULD occur in some

                                                replies - see 3.6.4



references      0*              1               SHOULD occur in some

                                                replies - see 3.6.4



subject         0               1



comments        0               unlimited



keywords        0               unlimited



optional-field  0               unlimited



   The exact interpretation of each field is described in subsequent

   sections.



3.6.1. The origination date field



   The origination date field consists of the field name "Date" followed

   by a date-time specification.



orig-date       =       "Date:" date-time CRLF



   The origination date specifies the date and time at which the creator

   of the message indicated that the message was complete and ready to

   enter the mail delivery system.  For instance, this might be the time

   that a user pushes the "send" or "submit" button in an application

   program.  In any case, it is specifically not intended to convey the

   time that the message is actually transported, but rather the time at

   which the human or other creator of the message has put the message

   into its final form, ready for transport.  (For example, a portable

   computer user who is not connected to a network might queue a message









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   for delivery.  The origination date is intended to contain the date

   and time that the user queued the message, not the time when the user

   connected to the network to send the message.)



3.6.2. Originator fields



   The originator fields of a message consist of the from field, the

   sender field (when applicable), and optionally the reply-to field.

   The from field consists of the field name "From" and a

   comma-separated list of one or more mailbox specifications.  If the

   from field contains more than one mailbox specification in the

   mailbox-list, then the sender field, containing the field name

   "Sender" and a single mailbox specification, MUST appear in the

   message.  In either case, an optional reply-to field MAY also be

   included, which contains the field name "Reply-To" and a

   comma-separated list of one or more addresses.



from            =       "From:" mailbox-list CRLF



sender          =       "Sender:" mailbox CRLF



reply-to        =       "Reply-To:" address-list CRLF



   The originator fields indicate the mailbox(es) of the source of the

   message.  The "From:" field specifies the author(s) of the message,

   that is, the mailbox(es) of the person(s) or system(s) responsible

   for the writing of the message.  The "Sender:" field specifies the

   mailbox of the agent responsible for the actual transmission of the

   message.  For example, if a secretary were to send a message for

   another person, the mailbox of the secretary would appear in the

   "Sender:" field and the mailbox of the actual author would appear in

   the "From:" field.  If the originator of the message can be indicated

   by a single mailbox and the author and transmitter are identical, the

   "Sender:" field SHOULD NOT be used.  Otherwise, both fields SHOULD

   appear.



   The originator fields also provide the information required when

   replying to a message.  When the "Reply-To:" field is present, it

   indicates the mailbox(es) to which the author of the message suggests

   that replies be sent.  In the absence of the "Reply-To:" field,

   replies SHOULD by default be sent to the mailbox(es) specified in the

   "From:" field unless otherwise specified by the person composing the

   reply.



   In all cases, the "From:" field SHOULD NOT contain any mailbox that

   does not belong to the author(s) of the message.  See also section

   3.6.3 for more information on forming the destination addresses for a

   reply.







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3.6.3. Destination address fields



   The destination fields of a message consist of three possible fields,

   each of the same form: The field name, which is either "To", "Cc", or

   "Bcc", followed by a comma-separated list of one or more addresses

   (either mailbox or group syntax).



to              =       "To:" address-list CRLF



cc              =       "Cc:" address-list CRLF



bcc             =       "Bcc:" (address-list / [CFWS]) CRLF



   The destination fields specify the recipients of the message.  Each

   destination field may have one or more addresses, and each of the

   addresses indicate the intended recipients of the message.  The only

   difference between the three fields is how each is used.



   The "To:" field contains the address(es) of the primary recipient(s)

   of the message.



   The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of

   making a copy on a typewriter using carbon paper) contains the

   addresses of others who are to receive the message, though the

   content of the message may not be directed at them.



   The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains

   addresses of recipients of the message whose addresses are not to be

   revealed to other recipients of the message.  There are three ways in

   which the "Bcc:" field is used.  In the first case, when a message

   containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is

   removed even though all of the recipients (including those specified

   in the "Bcc:" field) are sent a copy of the message.  In the second

   case, recipients specified in the "To:" and "Cc:" lines each are sent

   a copy of the message with the "Bcc:" line removed as above, but the

   recipients on the "Bcc:" line get a separate copy of the message

   containing a "Bcc:" line.  (When there are multiple recipient

   addresses in the "Bcc:" field, some implementations actually send a

   separate copy of the message to each recipient with a "Bcc:"

   containing only the address of that particular recipient.) Finally,

   since a "Bcc:" field may contain no addresses, a "Bcc:" field can be

   sent without any addresses indicating to the recipients that blind

   copies were sent to someone.  Which method to use with "Bcc:" fields

   is implementation dependent, but refer to the "Security

   Considerations" section of this document for a discussion of each.













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   When a message is a reply to another message, the mailboxes of the

   authors of the original message (the mailboxes in the "From:" field)

   or mailboxes specified in the "Reply-To:" field (if it exists) MAY

   appear in the "To:" field of the reply since these would normally be

   the primary recipients of the reply.  If a reply is sent to a message

   that has destination fields, it is often desirable to send a copy of

   the reply to all of the recipients of the message, in addition to the

   author.  When such a reply is formed, addresses in the "To:" and

   "Cc:" fields of the original message MAY appear in the "Cc:" field of

   the reply, since these are normally secondary recipients of the

   reply.  If a "Bcc:" field is present in the original message,

   addresses in that field MAY appear in the "Bcc:" field of the reply,

   but SHOULD NOT appear in the "To:" or "Cc:" fields.



   Note: Some mail applications have automatic reply commands that

   include the destination addresses of the original message in the

   destination addresses of the reply.  How those reply commands behave

   is implementation dependent and is beyond the scope of this document.

   In particular, whether or not to include the original destination

   addresses when the original message had a "Reply-To:" field is not

   addressed here.



3.6.4. Identification fields



   Though optional, every message SHOULD have a "Message-ID:" field.

   Furthermore, reply messages SHOULD have "In-Reply-To:" and

   "References:" fields as appropriate, as described below.



   The "Message-ID:" field contains a single unique message identifier.

   The "References:" and "In-Reply-To:" field each contain one or more

   unique message identifiers, optionally separated by CFWS.



   The message identifier (msg-id) is similar in syntax to an angle-addr

   construct without the internal CFWS.



message-id      =       "Message-ID:" msg-id CRLF



in-reply-to     =       "In-Reply-To:" 1*msg-id CRLF



references      =       "References:" 1*msg-id CRLF



msg-id          =       [CFWS] "<" id-left "@" id-right ">" [CFWS]



id-left         =       dot-atom-text / no-fold-quote / obs-id-left



id-right        =       dot-atom-text / no-fold-literal / obs-id-right



no-fold-quote   =       DQUOTE *(qtext / quoted-pair) DQUOTE







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no-fold-literal =       "[" *(dtext / quoted-pair) "]"



   The "Message-ID:" field provides a unique message identifier that

   refers to a particular version of a particular message.  The

   uniqueness of the message identifier is guaranteed by the host that

   generates it (see below).  This message identifier is intended to be

   machine readable and not necessarily meaningful to humans.  A message

   identifier pertains to exactly one instantiation of a particular

   message; subsequent revisions to the message each receive new message

   identifiers.



   Note: There are many instances when messages are "changed", but those

   changes do not constitute a new instantiation of that message, and

   therefore the message would not get a new message identifier.  For

   example, when messages are introduced into the transport system, they

   are often prepended with additional header fields such as trace

   fields (described in section 3.6.7) and resent fields (described in

   section 3.6.6).  The addition of such header fields does not change

   the identity of the message and therefore the original "Message-ID:"

   field is retained.  In all cases, it is the meaning that the sender

   of the message wishes to convey (i.e., whether this is the same

   message or a different message) that determines whether or not the

   "Message-ID:" field changes, not any particular syntactic difference

   that appears (or does not appear) in the message.



   The "In-Reply-To:" and "References:" fields are used when creating a

   reply to a message.  They hold the message identifier of the original

   message and the message identifiers of other messages (for example,

   in the case of a reply to a message which was itself a reply).  The

   "In-Reply-To:" field may be used to identify the message (or

   messages) to which the new message is a reply, while the

   "References:" field may be used to identify a "thread" of

   conversation.



   When creating a reply to a message, the "In-Reply-To:" and

   "References:" fields of the resultant message are constructed as

   follows:



   The "In-Reply-To:" field will contain the contents of the "Message-

   ID:" field of the message to which this one is a reply (the "parent

   message").  If there is more than one parent message, then the "In-

   Reply-To:" field will contain the contents of all of the parents'

   "Message-ID:" fields.  If there is no "Message-ID:" field in any of

   the parent messages, then the new message will have no "In-Reply-To:"

   field.













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   The "References:" field will contain the contents of the parent's

   "References:" field (if any) followed by the contents of the parent's

   "Message-ID:" field (if any).  If the parent message does not contain

   a "References:" field but does have an "In-Reply-To:" field

   containing a single message identifier, then the "References:" field

   will contain the contents of the parent's "In-Reply-To:" field

   followed by the contents of the parent's "Message-ID:" field (if

   any).  If the parent has none of the "References:", "In-Reply-To:",

   or "Message-ID:" fields, then the new message will have no

   "References:" field.



   Note: Some implementations parse the "References:" field to display

   the "thread of the discussion".  These implementations assume that

   each new message is a reply to a single parent and hence that they

   can walk backwards through the "References:" field to find the parent

   of each message listed there.  Therefore, trying to form a

   "References:" field for a reply that has multiple parents is

   discouraged and how to do so is not defined in this document.



   The message identifier (msg-id) itself MUST be a globally unique

   identifier for a message.  The generator of the message identifier

   MUST guarantee that the msg-id is unique.  There are several

   algorithms that can be used to accomplish this.  Since the msg-id has

   a similar syntax to angle-addr (identical except that comments and

   folding white space are not allowed), a good method is to put the

   domain name (or a domain literal IP address) of the host on which the

   message identifier was created on the right hand side of the "@", and

   put a combination of the current absolute date and time along with

   some other currently unique (perhaps sequential) identifier available

   on the system (for example, a process id number) on the left hand

   side.  Using a date on the left hand side and a domain name or domain

   literal on the right hand side makes it possible to guarantee

   uniqueness since no two hosts use the same domain name or IP address

   at the same time.  Though other algorithms will work, it is

   RECOMMENDED that the right hand side contain some domain identifier

   (either of the host itself or otherwise) such that the generator of

   the message identifier can guarantee the uniqueness of the left hand

   side within the scope of that domain.



   Semantically, the angle bracket characters are not part of the

   msg-id; the msg-id is what is contained between the two angle bracket

   characters.



















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3.6.5. Informational fields



   The informational fields are all optional.  The "Keywords:" field

   contains a comma-separated list of one or more words or

   quoted-strings. The "Subject:" and "Comments:" fields are

   unstructured fields as defined in section 2.2.1, and therefore may

   contain text or folding white space.



subject         =       "Subject:" unstructured CRLF



comments        =       "Comments:" unstructured CRLF



keywords        =       "Keywords:" phrase *("," phrase) CRLF



   These three fields are intended to have only human-readable content

   with information about the message.  The "Subject:" field is the most

   common and contains a short string identifying the topic of the

   message.  When used in a reply, the field body MAY start with the

   string "Re: " (from the Latin "res", in the matter of) followed by

   the contents of the "Subject:" field body of the original message.

   If this is done, only one instance of the literal string "Re: " ought

   to be used since use of other strings or more than one instance can

   lead to undesirable consequences.  The "Comments:" field contains any

   additional comments on the text of the body of the message.  The

   "Keywords:" field contains a comma-separated list of important words

   and phrases that might be useful for the recipient.



3.6.6. Resent fields



   Resent fields SHOULD be added to any message that is reintroduced by

   a user into the transport system.  A separate set of resent fields

   SHOULD be added each time this is done.  All of the resent fields

   corresponding to a particular resending of the message SHOULD be

   together.  Each new set of resent fields is prepended to the message;

   that is, the most recent set of resent fields appear earlier in the

   message.  No other fields in the message are changed when resent

   fields are added.



   Each of the resent fields corresponds to a particular field elsewhere

   in the syntax.  For instance, the "Resent-Date:" field corresponds to

   the "Date:" field and the "Resent-To:" field corresponds to the "To:"

   field.  In each case, the syntax for the field body is identical to

   the syntax given previously for the corresponding field.



   When resent fields are used, the "Resent-From:" and "Resent-Date:"

   fields MUST be sent.  The "Resent-Message-ID:" field SHOULD be sent.

   "Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be

   identical to "Resent-From:".







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resent-date     =       "Resent-Date:" date-time CRLF



resent-from     =       "Resent-From:" mailbox-list CRLF



resent-sender   =       "Resent-Sender:" mailbox CRLF



resent-to       =       "Resent-To:" address-list CRLF



resent-cc       =       "Resent-Cc:" address-list CRLF



resent-bcc      =       "Resent-Bcc:" (address-list / [CFWS]) CRLF



resent-msg-id   =       "Resent-Message-ID:" msg-id CRLF



   Resent fields are used to identify a message as having been

   reintroduced into the transport system by a user.  The purpose of

   using resent fields is to have the message appear to the final

   recipient as if it were sent directly by the original sender, with

   all of the original fields remaining the same.  Each set of resent

   fields correspond to a particular resending event.  That is, if a

   message is resent multiple times, each set of resent fields gives

   identifying information for each individual time.  Resent fields are

   strictly informational.  They MUST NOT be used in the normal

   processing of replies or other such automatic actions on messages.



   Note: Reintroducing a message into the transport system and using

   resent fields is a different operation from "forwarding".

   "Forwarding" has two meanings: One sense of forwarding is that a mail

   reading program can be told by a user to forward a copy of a message

   to another person, making the forwarded message the body of the new

   message.  A forwarded message in this sense does not appear to have

   come from the original sender, but is an entirely new message from

   the forwarder of the message.  On the other hand, forwarding is also

   used to mean when a mail transport program gets a message and

   forwards it on to a different destination for final delivery.  Resent

   header fields are not intended for use with either type of

   forwarding.



   The resent originator fields indicate the mailbox of the person(s) or

   system(s) that resent the message.  As with the regular originator

   fields, there are two forms: a simple "Resent-From:" form which

   contains the mailbox of the individual doing the resending, and the

   more complex form, when one individual (identified in the

   "Resent-Sender:" field) resends a message on behalf of one or more

   others (identified in the "Resent-From:" field).



   Note: When replying to a resent message, replies behave just as they

   would with any other message, using the original "From:",







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   "Reply-To:", "Message-ID:", and other fields.  The resent fields are

   only informational and MUST NOT be used in the normal processing of

   replies.



   The "Resent-Date:" indicates the date and time at which the resent

   message is dispatched by the resender of the message.  Like the

   "Date:" field, it is not the date and time that the message was

   actually transported.



   The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function

   identically to the "To:", "Cc:", and "Bcc:" fields respectively,

   except that they indicate the recipients of the resent message, not

   the recipients of the original message.



   The "Resent-Message-ID:" field provides a unique identifier for the

   resent message.



3.6.7. Trace fields



   The trace fields are a group of header fields consisting of an

   optional "Return-Path:" field, and one or more "Received:" fields.

   The "Return-Path:" header field contains a pair of angle brackets

   that enclose an optional addr-spec.  The "Received:" field contains a

   (possibly empty) list of name/value pairs followed by a semicolon and

   a date-time specification.  The first item of the name/value pair is

   defined by item-name, and the second item is either an addr-spec, an

   atom, a domain, or a msg-id.  Further restrictions may be applied to

   the syntax of the trace fields by standards that provide for their

   use, such as [RFC2821].



trace           =       [return]

                        1*received



return          =       "Return-Path:" path CRLF



path            =       ([CFWS] "<" ([CFWS] / addr-spec) ">" [CFWS]) /

                        obs-path



received        =       "Received:" name-val-list ";" date-time CRLF



name-val-list   =       [CFWS] [name-val-pair *(CFWS name-val-pair)]



name-val-pair   =       item-name CFWS item-value



item-name       =       ALPHA *(["-"] (ALPHA / DIGIT))



item-value      =       1*angle-addr / addr-spec /

                         atom / domain / msg-id







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   A full discussion of the Internet mail use of trace fields is

   contained in [RFC2821].  For the purposes of this standard, the trace

   fields are strictly informational, and any formal interpretation of

   them is outside of the scope of this document.



3.6.8. Optional fields



   Fields may appear in messages that are otherwise unspecified in this

   standard.  They MUST conform to the syntax of an optional-field.

   This is a field name, made up of the printable US-ASCII characters

   except SP and colon, followed by a colon, followed by any text which

   conforms to unstructured.



   The field names of any optional-field MUST NOT be identical to any

   field name specified elsewhere in this standard.



optional-field  =       field-name ":" unstructured CRLF



field-name      =       1*ftext



ftext           =       %d33-57 /               ; Any character except

                        %d59-126                ;  controls, SP, and

                                                ;  ":".



   For the purposes of this standard, any optional field is

   uninterpreted.



4. Obsolete Syntax



   Earlier versions of this standard allowed for different (usually more

   liberal) syntax than is allowed in this version.  Also, there have

   been syntactic elements used in messages on the Internet whose

   interpretation have never been documented.  Though some of these

   syntactic forms MUST NOT be generated according to the grammar in

   section 3, they MUST be accepted and parsed by a conformant receiver.

   This section documents many of these syntactic elements.  Taking the

   grammar in section 3 and adding the definitions presented in this

   section will result in the grammar to use for interpretation of

   messages.



   Note: This section identifies syntactic forms that any implementation

   MUST reasonably interpret.  However, there are certainly Internet

   messages which do not conform to even the additional syntax given in

   this section.  The fact that a particular form does not appear in any

   section of this document is not justification for computer programs

   to crash or for malformed data to be irretrievably lost by any

   implementation.  To repeat an example, though this document requires

   lines in messages to be no longer than 998 characters, silently







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   discarding the 999th and subsequent characters in a line without

   warning would still be bad behavior for an implementation.  It is up

   to the implementation to deal with messages robustly.



   One important difference between the obsolete (interpreting) and the

   current (generating) syntax is that in structured header field bodies

   (i.e., between the colon and the CRLF of any structured header

   field), white space characters, including folding white space, and

   comments can be freely inserted between any syntactic tokens.  This

   allows many complex forms that have proven difficult for some

   implementations to parse.



   Another key difference between the obsolete and the current syntax is

   that the rule in section 3.2.3 regarding lines composed entirely of

   white space in comments and folding white space does not apply.  See

   the discussion of folding white space in section 4.2 below.



   Finally, certain characters that were formerly allowed in messages

   appear in this section.  The NUL character (ASCII value 0) was once

   allowed, but is no longer for compatibility reasons.  CR and LF were

   allowed to appear in messages other than as CRLF; this use is also

   shown here.



   Other differences in syntax and semantics are noted in the following

   sections.



4.1. Miscellaneous obsolete tokens



   These syntactic elements are used elsewhere in the obsolete syntax or

   in the main syntax.  The obs-char and obs-qp elements each add ASCII

   value 0. Bare CR and bare LF are added to obs-text and obs-utext.

   The period character is added to obs-phrase. The obs-phrase-list

   provides for "empty" elements in a comma-separated list of phrases.



   Note: The "period" (or "full stop") character (".") in obs-phrase is

   not a form that was allowed in earlier versions of this or any other

   standard.  Period (nor any other character from specials) was not

   allowed in phrase because it introduced a parsing difficulty

   distinguishing between phrases and portions of an addr-spec (see

   section 4.4).  It appears here because the period character is

   currently used in many messages in the display-name portion of

   addresses, especially for initials in names, and therefore must be

   interpreted properly.  In the future, period may appear in the

   regular syntax of phrase.



obs-qp          =       "\" (%d0-127)



obs-text        =       *LF *CR *(obs-char *LF *CR)







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obs-char        =       %d0-9 / %d11 /          ; %d0-127 except CR and

                        %d12 / %d14-127         ;  LF



obs-utext       =       obs-text



obs-phrase      =       word *(word / "." / CFWS)



obs-phrase-list =       phrase / 1*([phrase] [CFWS] "," [CFWS]) [phrase]



   Bare CR and bare LF appear in messages with two different meanings.

   In many cases, bare CR or bare LF are used improperly instead of CRLF

   to indicate line separators.  In other cases, bare CR and bare LF are

   used simply as ASCII control characters with their traditional ASCII

   meanings.



4.2. Obsolete folding white space



   In the obsolete syntax, any amount of folding white space MAY be

   inserted where the obs-FWS rule is allowed.  This creates the

   possibility of having two consecutive "folds" in a line, and

   therefore the possibility that a line which makes up a folded header

   field could be composed entirely of white space.



   obs-FWS         =       1*WSP *(CRLF 1*WSP)



4.3. Obsolete Date and Time



   The syntax for the obsolete date format allows a 2 digit year in the

   date field and allows for a list of alphabetic time zone

   specifications that were used in earlier versions of this standard.

   It also permits comments and folding white space between many of the

   tokens.



obs-day-of-week =       [CFWS] day-name [CFWS]



obs-year        =       [CFWS] 2*DIGIT [CFWS]



obs-month       =       CFWS month-name CFWS



obs-day         =       [CFWS] 1*2DIGIT [CFWS]



obs-hour        =       [CFWS] 2DIGIT [CFWS]



obs-minute      =       [CFWS] 2DIGIT [CFWS]



obs-second      =       [CFWS] 2DIGIT [CFWS]



obs-zone        =       "UT" / "GMT" /          ; Universal Time







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                                                ; North American UT

                                                ; offsets

                        "EST" / "EDT" /         ; Eastern:  - 5/ - 4

                        "CST" / "CDT" /         ; Central:  - 6/ - 5

                        "MST" / "MDT" /         ; Mountain: - 7/ - 6

                        "PST" / "PDT" /         ; Pacific:  - 8/ - 7



                        %d65-73 /               ; Military zones - "A"

                        %d75-90 /               ; through "I" and "K"

                        %d97-105 /              ; through "Z", both

                        %d107-122               ; upper and lower case



   Where a two or three digit year occurs in a date, the year is to be

   interpreted as follows: If a two digit year is encountered whose

   value is between 00 and 49, the year is interpreted by adding 2000,

   ending up with a value between 2000 and 2049.  If a two digit year is

   encountered with a value between 50 and 99, or any three digit year

   is encountered, the year is interpreted by adding 1900.



   In the obsolete time zone, "UT" and "GMT" are indications of

   "Universal Time" and "Greenwich Mean Time" respectively and are both

   semantically identical to "+0000".



   The remaining three character zones are the US time zones.  The first

   letter, "E", "C", "M", or "P" stands for "Eastern", "Central",

   "Mountain" and "Pacific".  The second letter is either "S" for

   "Standard" time, or "D" for "Daylight" (or summer) time.  Their

   interpretations are as follows:



   EDT is semantically equivalent to -0400

   EST is semantically equivalent to -0500

   CDT is semantically equivalent to -0500

   CST is semantically equivalent to -0600

   MDT is semantically equivalent to -0600

   MST is semantically equivalent to -0700

   PDT is semantically equivalent to -0700

   PST is semantically equivalent to -0800



   The 1 character military time zones were defined in a non-standard

   way in [RFC822] and are therefore unpredictable in their meaning.

   The original definitions of the military zones "A" through "I" are

   equivalent to "+0100" through "+0900" respectively; "K", "L", and "M"

   are equivalent to  "+1000", "+1100", and "+1200" respectively; "N"

   through "Y" are equivalent to "-0100" through "-1200" respectively;

   and "Z" is equivalent to "+0000".  However, because of the error in

   [RFC822], they SHOULD all be considered equivalent to "-0000" unless

   there is out-of-band information confirming their meaning.









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   Other multi-character (usually between 3 and 5) alphabetic time zones

   have been used in Internet messages.  Any such time zone whose

   meaning is not known SHOULD be considered equivalent to "-0000"

   unless there is out-of-band information confirming their meaning.



4.4. Obsolete Addressing



   There are three primary differences in addressing.  First, mailbox

   addresses were allowed to have a route portion before the addr-spec

   when enclosed in "<" and ">".  The route is simply a comma-separated

   list of domain names, each preceded by "@", and the list terminated

   by a colon.  Second, CFWS were allowed between the period-separated

   elements of local-part and domain (i.e., dot-atom was not used).  In

   addition, local-part is allowed to contain quoted-string in addition

   to just atom.  Finally, mailbox-list and address-list were allowed to

   have "null" members.  That is, there could be two or more commas in

   such a list with nothing in between them.



obs-angle-addr  =       [CFWS] "<" [obs-route] addr-spec ">" [CFWS]



obs-route       =       [CFWS] obs-domain-list ":" [CFWS]



obs-domain-list =       "@" domain *(*(CFWS / "," ) [CFWS] "@" domain)



obs-local-part  =       word *("." word)



obs-domain      =       atom *("." atom)



obs-mbox-list   =       1*([mailbox] [CFWS] "," [CFWS]) [mailbox]



obs-addr-list   =       1*([address] [CFWS] "," [CFWS]) [address]



   When interpreting addresses, the route portion SHOULD be ignored.



4.5. Obsolete header fields



   Syntactically, the primary difference in the obsolete field syntax is

   that it allows multiple occurrences of any of the fields and they may

   occur in any order.  Also, any amount of white space is allowed

   before the ":" at the end of the field name.



obs-fields      =       *(obs-return /

                        obs-received /

                        obs-orig-date /

                        obs-from /

                        obs-sender /

                        obs-reply-to /

                        obs-to /







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                        obs-cc /

                        obs-bcc /

                        obs-message-id /

                        obs-in-reply-to /

                        obs-references /

                        obs-subject /

                        obs-comments /

                        obs-keywords /

                        obs-resent-date /

                        obs-resent-from /

                        obs-resent-send /

                        obs-resent-rply /

                        obs-resent-to /

                        obs-resent-cc /

                        obs-resent-bcc /

                        obs-resent-mid /

                        obs-optional)



   Except for destination address fields (described in section 4.5.3),

   the interpretation of multiple occurrences of fields is unspecified.

   Also, the interpretation of trace fields and resent fields which do

   not occur in blocks prepended to the message is unspecified as well.

   Unless otherwise noted in the following sections, interpretation of

   other fields is identical to the interpretation of their non-obsolete

   counterparts in section 3.



4.5.1. Obsolete origination date field



obs-orig-date   =       "Date" *WSP ":" date-time CRLF



4.5.2. Obsolete originator fields



obs-from        =       "From" *WSP ":" mailbox-list CRLF



obs-sender      =       "Sender" *WSP ":" mailbox CRLF



obs-reply-to    =       "Reply-To" *WSP ":" mailbox-list CRLF



4.5.3. Obsolete destination address fields



obs-to          =       "To" *WSP ":" address-list CRLF



obs-cc          =       "Cc" *WSP ":" address-list CRLF



obs-bcc         =       "Bcc" *WSP ":" (address-list / [CFWS]) CRLF













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   When multiple occurrences of destination address fields occur in a

   message, they SHOULD be treated as if the address-list in the first

   occurrence of the field is combined with the address lists of the

   subsequent occurrences by adding a comma and concatenating.



4.5.4. Obsolete identification fields



   The obsolete "In-Reply-To:" and "References:" fields differ from the

   current syntax in that they allow phrase (words or quoted strings) to

   appear.  The obsolete forms of the left and right sides of msg-id

   allow interspersed CFWS, making them syntactically identical to

   local-part and domain respectively.



obs-message-id  =       "Message-ID" *WSP ":" msg-id CRLF



obs-in-reply-to =       "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF



obs-references  =       "References" *WSP ":" *(phrase / msg-id) CRLF



obs-id-left     =       local-part



obs-id-right    =       domain



   For purposes of interpretation, the phrases in the "In-Reply-To:" and

   "References:" fields are ignored.



   Semantically, none of the optional CFWS surrounding the local-part

   and the domain are part of the obs-id-left and obs-id-right

   respectively.



4.5.5. Obsolete informational fields



obs-subject     =       "Subject" *WSP ":" unstructured CRLF



obs-comments    =       "Comments" *WSP ":" unstructured CRLF



obs-keywords    =       "Keywords" *WSP ":" obs-phrase-list CRLF



4.5.6. Obsolete resent fields



   The obsolete syntax adds a "Resent-Reply-To:" field, which consists

   of the field name, the optional comments and folding white space, the

   colon, and a comma separated list of addresses.



obs-resent-from =       "Resent-From" *WSP ":" mailbox-list CRLF



obs-resent-send =       "Resent-Sender" *WSP ":" mailbox CRLF









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obs-resent-date =       "Resent-Date" *WSP ":" date-time CRLF



obs-resent-to   =       "Resent-To" *WSP ":" address-list CRLF



obs-resent-cc   =       "Resent-Cc" *WSP ":" address-list CRLF



obs-resent-bcc  =       "Resent-Bcc" *WSP ":"

                         (address-list / [CFWS]) CRLF



obs-resent-mid  =       "Resent-Message-ID" *WSP ":" msg-id CRLF



obs-resent-rply =       "Resent-Reply-To" *WSP ":" address-list CRLF



   As with other resent fields, the "Resent-Reply-To:" field is to be

   treated as trace information only.



4.5.7. Obsolete trace fields



   The obs-return and obs-received are again given here as template

   definitions, just as return and received are in section 3.  Their

   full syntax is given in [RFC2821].



obs-return      =       "Return-Path" *WSP ":" path CRLF



obs-received    =       "Received" *WSP ":" name-val-list CRLF



obs-path        =       obs-angle-addr



4.5.8. Obsolete optional fields



obs-optional    =       field-name *WSP ":" unstructured CRLF



5. Security Considerations



   Care needs to be taken when displaying messages on a terminal or

   terminal emulator.  Powerful terminals may act on escape sequences

   and other combinations of ASCII control characters with a variety of

   consequences.  They can remap the keyboard or permit other

   modifications to the terminal which could lead to denial of service

   or even damaged data.  They can trigger (sometimes programmable)

   answerback messages which can allow a message to cause commands to be

   issued on the recipient's behalf.  They can also effect the operation

   of terminal attached devices such as printers.  Message viewers may

   wish to strip potentially dangerous terminal escape sequences from

   the message prior to display.  However, other escape sequences appear

   in messages for useful purposes (cf. [RFC2045, RFC2046, RFC2047,

   RFC2048, RFC2049, ISO2022]) and therefore should not be stripped

   indiscriminately.







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   Transmission of non-text objects in messages raises additional

   security issues.  These issues are discussed in [RFC2045, RFC2046,

   RFC2047, RFC2048, RFC2049].



   Many implementations use the "Bcc:" (blind carbon copy) field

   described in section 3.6.3 to facilitate sending messages to

   recipients without revealing the addresses of one or more of the

   addressees to the other recipients.  Mishandling this use of "Bcc:"

   has implications for confidential information that might be revealed,

   which could eventually lead to security problems through knowledge of

   even the existence of a particular mail address.  For example, if

   using the first method described in section 3.6.3, where the "Bcc:"

   line is removed from the message, blind recipients have no explicit

   indication that they have been sent a blind copy, except insofar as

   their address does not appear in the message header.  Because of

   this, one of the blind addressees could potentially send a reply to

   all of the shown recipients and accidentally reveal that the message

   went to the blind recipient.  When the second method from section

   3.6.3 is used, the blind recipient's address appears in the "Bcc:"

   field of a separate copy of the message. If the "Bcc:" field sent

   contains all of the blind addressees, all of the "Bcc:" recipients

   will be seen by each "Bcc:" recipient.  Even if a separate message is

   sent to each "Bcc:" recipient with only the individual's address,

   implementations still need to be careful to process replies to the

   message as per section 3.6.3 so as not to accidentally reveal the

   blind recipient to other recipients.



6. Bibliography



   [ASCII]    American National Standards Institute (ANSI), Coded

              Character Set - 7-Bit American National Standard Code for

              Information Interchange, ANSI X3.4, 1986.



   [ISO2022] International Organization for Standardization (ISO),

              Information processing - ISO 7-bit and 8-bit coded

              character sets - Code extension techniques, Third edition

              - 1986-05-01, ISO 2022, 1986.



   [RFC822]   Crocker, D., "Standard for the Format of ARPA Internet

              Text Messages", RFC 822, August 1982.



   [RFC2045]  Freed, N. and  N. Borenstein, "Multipurpose Internet Mail

              Extensions (MIME) Part One: Format of Internet Message

              Bodies", RFC 2045, November 1996.



   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail

              Extensions (MIME) Part Two: Media Types", RFC 2046,

              November 1996.







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   [RFC2047]  Moore, K., "Multipurpose Internet Mail Extensions (MIME)

              Part Three: Message Header Extensions for Non-ASCII Text",

              RFC 2047, November 1996.



   [RFC2048]  Freed, N., Klensin, J. and J. Postel, "Multipurpose

              Internet Mail Extensions (MIME) Part Four: Format of

              Internet Message Bodies", RFC 2048, November 1996.



   [RFC2049]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail

              Extensions (MIME) Part Five: Conformance Criteria and

              Examples", RFC 2049, November 1996.



   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate

              Requirement Levels", BCP 14, RFC 2119, March 1997.



   [RFC2234]  Crocker, D., Editor, and P. Overell, "Augmented BNF for

              Syntax Specifications: ABNF", RFC 2234, November 1997.



   [RFC2821]  Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC

              2821, March 2001.



   [STD3]     Braden, R., "Host Requirements", STD 3, RFC 1122 and RFC

              1123, October 1989.



   [STD12]    Mills, D., "Network Time Protocol", STD 12, RFC 1119,

              September 1989.



   [STD13]    Mockapetris, P., "Domain Name System", STD 13, RFC 1034

              and RFC 1035,  November 1987.



   [STD14]    Partridge, C., "Mail Routing and the Domain System", STD

              14, RFC 974, January 1986.



7. Editor's Address



   Peter W. Resnick

   QUALCOMM Incorporated

   5775 Morehouse Drive

   San Diego, CA 92121-1714

   USA



   Phone: +1 858 651 4478

   Fax:   +1 858 651 1102

   EMail: presnick@qualcomm.com















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8. Acknowledgements



   Many people contributed to this document.  They included folks who

   participated in the Detailed Revision and Update of Messaging

   Standards (DRUMS) Working Group of the Internet Engineering Task

   Force (IETF), the chair of DRUMS, the Area Directors of the IETF, and

   people who simply sent their comments in via e-mail.  The editor is

   deeply indebted to them all and thanks them sincerely.  The below

   list includes everyone who sent e-mail concerning this document.

   Hopefully, everyone who contributed is named here:



   Matti Aarnio              Barry Finkel           Larry Masinter

   Tanaka Akira              Erik Forsberg          Denis McKeon

   Russ Allbery              Chuck Foster           William P McQuillan

   Eric Allman               Paul Fox               Alexey Melnikov

   Harald Tveit Alvestrand   Klaus M. Frank         Perry E. Metzger

   Ran Atkinson              Ned Freed              Steven Miller

   Jos Backus                Jochen Friedrich       Keith Moore

   Bruce Balden              Randall C. Gellens     John Gardiner Myers

   Dave Barr                 Sukvinder Singh Gill   Chris Newman

   Alan Barrett              Tim Goodwin            John W. Noerenberg

   John Beck                 Philip Guenther        Eric Norman

   J. Robert von Behren      Tony Hansen            Mike O'Dell

   Jos den Bekker            John Hawkinson         Larry Osterman

   D. J. Bernstein           Philip Hazel           Paul Overell

   James Berriman            Kai Henningsen         Jacob Palme

   Norbert Bollow            Robert Herriot         Michael A. Patton

   Raj Bose                  Paul Hethmon           Uzi Paz

   Antony Bowesman           Jim Hill               Michael A. Quinlan

   Scott Bradner             Paul E. Hoffman        Eric S. Raymond

   Randy Bush                Steve Hole             Sam Roberts

   Tom Byrer                 Kari Hurtta            Hugh Sasse

   Bruce Campbell            Marco S. Hyman         Bart Schaefer

   Larry Campbell            Ofer Inbar             Tom Scola

   W. J. Carpenter           Olle Jarnefors         Wolfgang Segmuller

   Michael Chapman           Kevin Johnson          Nick Shelness

   Richard Clayton           Sudish Joseph          John Stanley

   Maurizio Codogno          Maynard Kang           Einar Stefferud

   Jim Conklin               Prabhat Keni           Jeff Stephenson

   R. Kelley Cook            John C. Klensin        Bernard Stern

   Steve Coya                Graham Klyne           Peter Sylvester

   Mark Crispin              Brad Knowles           Mark Symons

   Dave Crocker              Shuhei Kobayashi       Eric Thomas

   Matt Curtin               Peter Koch             Lee Thompson

   Michael D'Errico          Dan Kohn               Karel De Vriendt

   Cyrus Daboo               Christian Kuhtz        Matthew Wall

   Jutta Degener             Anand Kumria           Rolf Weber

   Mark Delany               Steen Larsen           Brent B. Welch







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   Steve Dorner              Eliot Lear             Dan Wing

   Harold A. Driscoll        Barry Leiba            Jack De Winter

   Michael Elkins            Jay Levitt             Gregory J. Woodhouse

   Robert Elz                Lars-Johan Liman       Greg A. Woods

   Johnny Eriksson           Charles Lindsey        Kazu Yamamoto

   Erik E. Fair              Pete Loshin            Alain Zahm

   Roger Fajman              Simon Lyall            Jamie Zawinski

   Patrik Faltstrom          Bill Manning           Timothy S. Zurcher

   Claus Andre Farber        John Martin





















































































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Appendix A. Example messages



   This section presents a selection of messages.  These are intended to

   assist in the implementation of this standard, but should not be

   taken as normative; that is to say, although the examples in this

   section were carefully reviewed, if there happens to be a conflict

   between these examples and the syntax described in sections 3 and 4

   of this document, the syntax in those sections is to be taken as

   correct.



   Messages are delimited in this section between lines of "----".  The

   "----" lines are not part of the message itself.



A.1. Addressing examples



   The following are examples of messages that might be sent between two

   individuals.



A.1.1. A message from one person to another with simple addressing



   This could be called a canonical message.  It has a single author,

   John Doe, a single recipient, Mary Smith, a subject, the date, a

   message identifier, and a textual message in the body.



----

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----



































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   If John's secretary Michael actually sent the message, though John

   was the author and replies to this message should go back to him, the

   sender field would be used:



----

From: John Doe <jdoe@machine.example>

Sender: Michael Jones <mjones@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----



A.1.2. Different types of mailboxes



   This message includes multiple addresses in the destination fields

   and also uses several different forms of addresses.



----

From: "Joe Q. Public" <john.q.public@example.com>

To: Mary Smith <mary@x.test>, jdoe@example.org, Who? <one@y.test>

Cc: <boss@nil.test>, "Giant; \"Big\" Box" <sysservices@example.net>

Date: Tue, 1 Jul 2003 10:52:37 +0200

Message-ID: <5678.21-Nov-1997@example.com>



Hi everyone.

----



   Note that the display names for Joe Q. Public and Giant; "Big" Box

   needed to be enclosed in double-quotes because the former contains

   the period and the latter contains both semicolon and double-quote

   characters (the double-quote characters appearing as quoted-pair

   construct).  Conversely, the display name for Who? could appear

   without them because the question mark is legal in an atom.  Notice

   also that jdoe@example.org and boss@nil.test have no display names

   associated with them at all, and jdoe@example.org uses the simpler

   address form without the angle brackets.























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A.1.3. Group addresses



----

From: Pete <pete@silly.example>

To: A Group:Chris Jones <c@a.test>,joe@where.test,John <jdoe@one.test>;

Cc: Undisclosed recipients:;

Date: Thu, 13 Feb 1969 23:32:54 -0330

Message-ID: <testabcd.1234@silly.example>



Testing.

----



   In this message, the "To:" field has a single group recipient named A

   Group which contains 3 addresses, and a "Cc:" field with an empty

   group recipient named Undisclosed recipients.



A.2. Reply messages



   The following is a series of three messages that make up a

   conversation thread between John and Mary.  John firsts sends a

   message to Mary, Mary then replies to John's message, and then John

   replies to Mary's reply message.



   Note especially the "Message-ID:", "References:", and "In-Reply-To:"

   fields in each message.



----

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----































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   When sending replies, the Subject field is often retained, though

   prepended with "Re: " as described in section 3.6.5.



----

From: Mary Smith <mary@example.net>

To: John Doe <jdoe@machine.example>

Reply-To: "Mary Smith: Personal Account" <smith@home.example>

Subject: Re: Saying Hello

Date: Fri, 21 Nov 1997 10:01:10 -0600

Message-ID: <3456@example.net>

In-Reply-To: <1234@local.machine.example>

References: <1234@local.machine.example>



This is a reply to your hello.

----



   Note the "Reply-To:" field in the above message.  When John replies

   to Mary's message above, the reply should go to the address in the

   "Reply-To:" field instead of the address in the "From:" field.



----

To: "Mary Smith: Personal Account" <smith@home.example>

From: John Doe <jdoe@machine.example>

Subject: Re: Saying Hello

Date: Fri, 21 Nov 1997 11:00:00 -0600

Message-ID: <abcd.1234@local.machine.tld>

In-Reply-To: <3456@example.net>

References: <1234@local.machine.example> <3456@example.net>



This is a reply to your reply.

----



A.3. Resent messages



   Start with the message that has been used as an example several

   times:



----

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----









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   Say that Mary, upon receiving this message, wishes to send a copy of

   the message to Jane such that (a) the message would appear to have

   come straight from John; (b) if Jane replies to the message, the

   reply should go back to John; and (c) all of the original

   information, like the date the message was originally sent to Mary,

   the message identifier, and the original addressee, is preserved.  In

   this case, resent fields are prepended to the message:



----

Resent-From: Mary Smith <mary@example.net>

Resent-To: Jane Brown <j-brown@other.example>

Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800

Resent-Message-ID: <78910@example.net>

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----



   If Jane, in turn, wished to resend this message to another person,

   she would prepend her own set of resent header fields to the above

   and send that.



















































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A.4. Messages with trace fields



   As messages are sent through the transport system as described in

   [RFC2821], trace fields are prepended to the message.  The following

   is an example of what those trace fields might look like.  Note that

   there is some folding white space in the first one since these lines

   can be long.



----

Received: from x.y.test

   by example.net

   via TCP

   with ESMTP

   id ABC12345

   for <mary@example.net>;  21 Nov 1997 10:05:43 -0600

Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: Fri, 21 Nov 1997 09:55:06 -0600

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----





















































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A.5. White space, comments, and other oddities



   White space, including folding white space, and comments can be

   inserted between many of the tokens of fields.  Taking the example

   from A.1.3, white space and comments can be inserted into all of the

   fields.



----

From: Pete(A wonderful \) chap) <pete(his account)@silly.test(his host)>

To:A Group(Some people)

     :Chris Jones <c@(Chris's host.)public.example>,

         joe@example.org,

  John <jdoe@one.test> (my dear friend); (the end of the group)

Cc:(Empty list)(start)Undisclosed recipients  :(nobody(that I know))  ;

Date: Thu,

      13

        Feb

          1969

      23:32

               -0330 (Newfoundland Time)

Message-ID:              <testabcd.1234@silly.test>



Testing.

----



   The above example is aesthetically displeasing, but perfectly legal.

   Note particularly (1) the comments in the "From:" field (including

   one that has a ")" character appearing as part of a quoted-pair); (2)

   the white space absent after the ":" in the "To:" field as well as

   the comment and folding white space after the group name, the special

   character (".") in the comment in Chris Jones's address, and the

   folding white space before and after "joe@example.org,"; (3) the

   multiple and nested comments in the "Cc:" field as well as the

   comment immediately following the ":" after "Cc"; (4) the folding

   white space (but no comments except at the end) and the missing

   seconds in the time of the date field; and (5) the white space before

   (but not within) the identifier in the "Message-ID:" field.



A.6. Obsoleted forms



   The following are examples of obsolete (that is, the "MUST NOT

   generate") syntactic elements described in section 4 of this

   document.

















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A.6.1. Obsolete addressing



   Note in the below example the lack of quotes around Joe Q. Public,

   the route that appears in the address for Mary Smith, the two commas

   that appear in the "To:" field, and the spaces that appear around the

   "." in the jdoe address.



----

From: Joe Q. Public <john.q.public@example.com>

To: Mary Smith <@machine.tld:mary@example.net>, , jdoe@test   . example

Date: Tue, 1 Jul 2003 10:52:37 +0200

Message-ID: <5678.21-Nov-1997@example.com>



Hi everyone.

----



A.6.2. Obsolete dates



   The following message uses an obsolete date format, including a non-

   numeric time zone and a two digit year.  Note that although the

   day-of-week is missing, that is not specific to the obsolete syntax;

   it is optional in the current syntax as well.



----

From: John Doe <jdoe@machine.example>

To: Mary Smith <mary@example.net>

Subject: Saying Hello

Date: 21 Nov 97 09:55:06 GMT

Message-ID: <1234@local.machine.example>



This is a message just to say hello.

So, "Hello".

----



A.6.3. Obsolete white space and comments



   White space and comments can appear between many more elements than

   in the current syntax.  Also, folding lines that are made up entirely

   of white space are legal.

























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----

From  : John Doe <jdoe@machine(comment).  example>

To    : Mary Smith

__

          <mary@example.net>

Subject     : Saying Hello

Date  : Fri, 21 Nov 1997 09(comment):   55  :  06 -0600

Message-ID  : <1234   @   local(blah)  .machine .example>



This is a message just to say hello.

So, "Hello".

----



   Note especially the second line of the "To:" field.  It starts with

   two space characters.  (Note that "__" represent blank spaces.)

   Therefore, it is considered part of the folding as described in

   section 4.2.  Also, the comments and white space throughout

   addresses, dates, and message identifiers are all part of the

   obsolete syntax.



Appendix B. Differences from earlier standards



   This appendix contains a list of changes that have been made in the

   Internet Message Format from earlier standards, specifically [RFC822]

   and [STD3].  Items marked with an asterisk (*) below are items which

   appear in section 4 of this document and therefore can no longer be

   generated.



   1. Period allowed in obsolete form of phrase.

   2. ABNF moved out of document to [RFC2234].

   3. Four or more digits allowed for year.

   4. Header field ordering (and lack thereof) made explicit.

   5. Encrypted header field removed.

   6. Received syntax loosened to allow any token/value pair.

   7. Specifically allow and give meaning to "-0000" time zone.

   8. Folding white space is not allowed between every token.

   9. Requirement for destinations removed.

   10. Forwarding and resending redefined.

   11. Extension header fields no longer specifically called out.

   12. ASCII 0 (null) removed.*

   13. Folding continuation lines cannot contain only white space.*

   14. Free insertion of comments not allowed in date.*

   15. Non-numeric time zones not allowed.*

   16. Two digit years not allowed.*

   17. Three digit years interpreted, but not allowed for generation.

   18. Routes in addresses not allowed.*

   19. CFWS within local-parts and domains not allowed.*

   20. Empty members of address lists not allowed.*







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   21. Folding white space between field name and colon not allowed.*

   22. Comments between field name and colon not allowed.

   23. Tightened syntax of in-reply-to and references.*

   24. CFWS within msg-id not allowed.*

   25. Tightened semantics of resent fields as informational only.

   26. Resent-Reply-To not allowed.*

   27. No multiple occurrences of fields (except resent and received).*

   28. Free CR and LF not allowed.*

   29. Routes in return path not allowed.*

   30. Line length limits specified.

   31. Bcc more clearly specified.



Appendix C. Notices



   Intellectual Property



   The IETF takes no position regarding the validity or scope of any

   intellectual property or other rights that might be claimed to

   pertain to the implementation or use of the technology described in

   this document or the extent to which any license under such rights

   might or might not be available; neither does it represent that it

   has made any effort to identify any such rights.  Information on the

   IETF's procedures with respect to rights in standards-track and

   standards-related documentation can be found in BCP-11.  Copies of

   claims of rights made available for publication and any assurances of

   licenses to be made available, or the result of an attempt made to

   obtain a general license or permission for the use of such

   proprietary rights by implementors or users of this specification can

   be obtained from the IETF Secretariat.













































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Full Copyright Statement



   Copyright (C) The Internet Society (2001).  All Rights Reserved.



   This document and translations of it may be copied and furnished to

   others, and derivative works that comment on or otherwise explain it

   or assist in its implementation may be prepared, copied, published

   and distributed, in whole or in part, without restriction of any

   kind, provided that the above copyright notice and this paragraph are

   included on all such copies and derivative works.  However, this

   document itself may not be modified in any way, such as by removing

   the copyright notice or references to the Internet Society or other

   Internet organizations, except as needed for the purpose of

   developing Internet standards in which case the procedures for

   copyrights defined in the Internet Standards process must be

   followed, or as required to translate it into languages other than

   English.



   The limited permissions granted above are perpetual and will not be

   revoked by the Internet Society or its successors or assigns.



   This document and the information contained herein is provided on an

   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.



Acknowledgement



   Funding for the RFC Editor function is currently provided by the

   Internet Society.







































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