RFC0733: Standard for the format of ARPA network text messages
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Obsoletes:
RFC0724
Obsoleted By:
RFC0822
RFC # 733
NIC # 41952
Obsoletes: RFC #561 (NIC #18516)
RFC #680 (NIC #32116)
RFC #724 (NIC #37435)
STANDARD FOR THE FORMAT OF
ARPA NETWORK TEXT MESSAGES(1)
21 November 1977
by
David H. Crocker
The Rand Corporation
John J. Vittal
Bolt Beranek and Newman Inc.
Kenneth T. Pogran
Massachusets Institute of Technology
D. Austin Henderson, Jr.(2)
Bolt Beranek and Newman Inc.
_________________________________________________________________
(1)This work was supported by the Defense Advanced Research
Projects Agency of the Department of Defense, under contract Nos.
N00014-75-C-0661, MDA903-76-C-0212, and DAHC15-73-C0181.
(2)The authors' postal addresses are: D. Crocker, The Rand
Corporation, Information Sciences Dept., 1700 Main St., Santa
Monica, California 90406; J. Vittal & D. A. Henderson, Bolt
Beranek & Newman, 50 Moulton St., Cambridge, Massachusetts 02138;
and K. Pogran, MIT Laboratory for Computer Science, 545
Technology Square, Cambridge, Massachusetts 02139. The authors'
ARPANET addresses are: DCrocker at Rand-Unix, Vittal at BBN-
TenexD, Pogran at MIT-Multics, and Henderson at BBN-TenexD.
-iii-
PREFACE
ARPA's Committee on Computer-Aided Human Communication
(CAHCOM) wishes to promulgate a standard for the format of ARPA
Network text message (mail) headers which will reasonably meet
the needs of the various message service subsystems on the
Network today. The authors of this document constitute the
CAHCOM subcommittee charged with the task of developing this new
standard.
Essentially, we specify a revision to ARPANET Request for
Comments (RFC) 561, "Standardizing Network Mail Headers", and RFC
680, "Message Transmission Protocol". This revision removes and
compacts portions of the previous syntax and adds several
features to network address specification. In particular, we
focus on people and not mailboxes as recipients and allow
reference to stored address lists. We expect this syntax to
provide sufficient capabilities to meet most users' immediate
needs and, therefore, give developers enough breathing room to
produce a new mail transmission protocol "properly". We believe
that there is enough of a consensus in the Network community in
favor of such a standard syntax to make possible its adoption at
this time. An earlier draft of this specification was published
as RFC #724, "Proposed Official Standard for the Format of ARPA
Network Messages" and contained extensive discussion of the
background and issues in ARPANET mail standards.
This specification was developed over the course of one
year, using the ARPANET mail environment, itself, to provide an
on-going forum for discussing the capabilities to be included.
More than twenty individuals, from across the country,
participated in this discussion and we would like to acknowledge
their considerable efforts. The syntax of the standard was
originally specified in the Backus-Naur Form (BNF) meta-language.
Ken L. Harrenstien, of SRI International, was responsible for
re-coding the BNF into an augmented BNF which compacts the
specification and allows increased comprehensibility.
-v-
CONTENTS
PREFACE..................................................... iii
Section
I. INTRODUCTION......................................... 1
II. FRAMEWORK............................................ 2
III. SYNTAX............................................... 4
A. Notational Conventions............................ 4
B. Lexical Analysis of Messages...................... 5
C. General Syntax of Messages........................ 13
D. Syntax of General Addressee Items................. 15
E. Supporting Constructs............................. 15
IV. SEMANTICS............................................ 17
A. Address Fields.................................... 17
B. Reference Specification Fields.................... 22
C. Other Fields and Syntactic Items.................. 23
D. Dates and Times................................... 24
V. EXAMPLES............................................. 25
A. Addresses......................................... 25
B. Address Lists..................................... 26
C. Originator Items.................................. 26
D. Complete Headers.................................. 28
Appendix
A. ALPHABETICAL LISTING OF SYNTAX RULES................. 31
B. SIMPLE PARSING....................................... 35
BIBLIOGRAPHY................................................ 37
Standard for the Format of Text Messages 1
I. Introduction
I. INTRODUCTION
This standard specifies a syntax for text messages which are
passed between computer users within the framework of "electronic
mail". The standard supersedes the informal standards specified
in ARPANET Request for Comments numbers 561, "Standardizing
Network Mail Headers", and 680, "Message Transmission Protocol".
In this document, a general framework is first described; the
formal syntax is then specified, followed by a discussion of the
semantics. Finally, a number of examples are given.
This specification is intended strictly as a definition of
what is to be passed between hosts on the ARPANET. It is NOT
intended to dictate either features which systems on the Network
are expected to support, or user interfaces to message creating
or reading programs.
A distinction should be made between what the specification
REQUIRES and what it ALLOWS. Messages can be made complex and
rich with formally-structured components of information or can be
kept small and simple, with a minimum of such information. Also,
the standard simplifies the interpretation of differing visual
formats in messages. These simplifications facilitate the formal
specification and indicate what the OFFICIAL semantics are for
messages. Only the visual aspect of a message is affected and
not the interpretation of information within it. Implementors
may choose to retain such visual distinctions.
Standard for the Format of Text Messages 2
II. Framework
II. FRAMEWORK
Since there are many message systems which exist outside the
ARPANET environment, as well as those within it, it may be useful
to consider the general framework, and resulting capabilities and
limitations, provided by this standard.
Messages are expected to consist of lines of text. No
special provisions are made, at this time, for encoding drawings,
facsimile, speech, or structured text.
No significant consideration has been given to questions of
data compression or transmission/storage efficiency. The
standard, in fact, tends to be very free with the number of bits
consumed. For example, field names are specified as free text,
rather than special terse codes.
A general "memo" framework is used. That is, a message
consists of some information, in a rigid format, followed by the
main part of the message, which is text and whose format is not
specified in this document. The syntax of several fields of the
rigidly-formated ("header") section is defined in this
specification; some of the header fields must be included in all
messages. The syntax which distinguishes between headers is
specified separately from the internal syntax for particular
headers. This separation is intended to allow extremely simple
parsers to operate on the overall structure of messages, without
concern for the detailed structure of individual headers.
Appendix B is provided to facilitate construction of these simple
parsers. In addition to the fields specified in this document,
it is expected that other fields will gain common use. User-
defined header fields allow systems to extend their functionality
while maintaining a uniform framework. The approach is similar
to that of the TELNET protocol, in that a basic standard is
defined which includes a mechanism for (optionally) extending
itself. As necessary, the authors of this document will regulate
the publishing of specifications for these "extension-fields",
through the same mechanisms used to publish this document.
Such a framework severely constrains document tone and
appearance and is primarily useful for most intra-organization
communications and relatively structured inter-organization
communication. A more robust environment might allow for multi-
font, multi-color, multi-dimension encoding of information. A
less robust environment, as is present in most single-machine
message systems, would more severely constrain the ability to add
fields and the decision to include specific fields. In contrast
to paper-based communication, it is interesting to note that the
Standard for the Format of Text Messages 3
II. Framework
RECEIVER of a message can exercise an extraordinary amount of
control over the message's appearance. The amount of actual
control available to message receivers is contingent upon the
capabilities of their individual message systems.
Standard for the Format of Text Messages 4
III. Syntax
III. SYNTAX
This syntax is given in five parts. The first part
describes the notation used in the specification. The second
part describes the base-level lexical analyzers which feed the
higher-level parser described in the succeeding sections. The
third part gives a general syntax for messages and standard
header fields; and the fourth part specifies the syntax of
addresses. A final part specifies some general syntax which
supports the other sections.
A. NOTATIONAL CONVENTIONS
These specifications are made in an augmented Backus-Naur Form
(BNF). Differences from standard BNF involve the naming of
rules, the indication of repetition and of "local" alternatives.
1. Rule naming
Angle brackets ("<", ">") are not used, in general. The name of
a rule is simply the name itself, rather than "<name>".
Quotation-marks enclose literal text (which may be upper and/or
lower case). Certain basic rules are in uppercase, such as
SPACE, TAB, CRLF, DIGIT, ALPHA, etc. Angle brackets are used in
rule definitions, and in the rest of this document, whenever
their presence will facilitate discerning the use of rule names.
2. Parentheses: Local alternatives
Elements enclosed in parentheses are treated as a single element.
Thus, "(elem (foo / bar) elem)" allows "(elem foo elem)" and
"(elem bar elem)".
3. * construct: Repetition
The character "*" preceding an element indicates repetition. The
full form is:
<l>*<m>element
indicating at least <l> and at most <m> occurrences of element.
Default values are 0 and infinity so that "*(element)" allows any
number, including zero; "1*element" requires at least one; and
"1*2element" allows one or two.
Standard for the Format of Text Messages 5
III. Syntax
A. Notational Conventions
4. <number>element
"<n>(element)" is equivalent to "<n>*<n>(element)"; that is,
exactly <n> occurrences of (element). Thus 2DIGIT is a 2-digit
number, and 3ALPHA is a string of three alphabetic characters.
5. # construct: Lists
A construct "#" is defined, similar to "*", as follows:
<l>#<m>element
indicating at least <l> and at most <m> elements, each separated
by one or more commas (","). This makes the usual form of lists
very easy; a rule such as '(element *("," element))' can be shown
as "1#element". Wherever this construct is used, null elements
are allowed, but do not contribute to the count of elements
present. That is, "(element),,(element)" is permitted, but
counts as only two elements. Therefore, where at least one
element is required, at least one non-null element must be
present.
6. [optional]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".
7. ; Comments
A semi-colon, set off some distance to the right of rule text,
starts a comment which continues to the end of line. This is a
simple way of including useful notes in parallel with the
specifications.
B. LEXICAL ANALYSIS OF MESSAGES
1. General Description
A message consists of headers and, optionally, a body (i.e. a
series of text lines). The text part is just a sequence of lines
containing ASCII characters; it is separated from the headers by
a null line (i.e., a line with nothing preceding the CRLF).
Standard for the Format of Text Messages 6
III. Syntax
B. Lexical Analysis
a. Folding and unfolding of headers
Each header item can be viewed as a single, logical line of
ASCII characters. For convenience, the field-body portion of
this conceptual entity can be split into a multiple-line
representation (i.e., "folded"). The general rule is that
wherever there can be linear-white-space (NOT simply LWSP-
chars), a CRLF immediately followed by AT LEAST one LWSP-char
can instead be inserted. (However, a header's name and the
following colon (":"), which occur at the beginning of the
header item, may NOT be folded onto multiple lines.) Thus,
the single line
To: "Joe Dokes & J. Harvey" <ddd at Host>, JJV at BBN
can be represented as
To: "Joe Dokes & J. Harvey" <ddd at Host>,
JJV at BBN
and
To: "Joe Dokes & J. Harvey"
<ddd at Host>,
JJV at BBN
and
To: "Joe Dokes
& J. Harvey" <ddd at Host>, JJV at BBN
The process of moving from this folded multiple-line
representation of a header field to its single line
representation will be called "unfolding". Unfolding is
accomplished by regarding CRLF immediately followed by a
LWSP-char as equivalent to the LWSP-char.
b. Structure of header fields
Once header fields have been unfolded, they may be viewed as
being composed of a field-name followed by a colon (":"),
followed by a field-body. The field-name must be composed of
printable ASCII characters (i.e., characters which have
values between 33. and 126., decimal, except colon) and
LWSP-chars. The field-body may be composed of any ASCII
characters (other than an unquoted CRLF, which has been
removed by unfolding).
Certain field-bodies of header fields may be interpreted
according to an internal syntax which some systems may wish
to parse. These fields will be referred to as "structured"
fields. Examples include fields containing dates and
Standard for the Format of Text Messages 7
III. Syntax
B. Lexical Analysis
addresses. Other fields, such as "Subject" and "Comments",
are regarded simply as strings of text.
NOTE: Field-names, unstructured field bodies and structured
field bodies each are scanned by their own, INDEPENDENT
"lexical" analyzer.
c. Field-names
To aid in the creation and reading of field-names, the free
insertion of LWSP-chars is allowed in reasonable places.
Rather than obscuring the syntax specification for field-name
with the explicit syntax for these LWSP-chars, the existence
of a "lexical" analyzer is assumed. The analyzer interprets
the text which comprises the field-name as a sequence of
field-name atoms (fnatoms) separated by LWSP-chars
Note that ONLY LWSP-chars may occur between the fnatoms of a
field-name and that CRLFs may NOT. In addition, comments are
NOT lexically recognized, as such, but parenthesized strings
are legal as part of field-names. These constraints are
different from what is permissible within structured field
bodies. In particular, this means that header field-names
must wholly occur on the FIRST line of a folded header item
and may NOT be split across two or more lines.
d. Unstructured field bodies
For some fields, such as "Subject" and "Comments", no
structuring is assumed; and they are treated simply as texts,
like those in the message body. Rules of folding apply to
these fields, so that such field bodies which occupy several
lines must therefore have the second and successive lines
indented by at least one LWSP-char.
e. Structured field bodies
To aid in the creation and reading of structured fields, the
free insertion of linear-white-space (which permits folding
by inclusion of CRLFs) is allowed in reasonable places.
Rather than obscuring the syntax specifications for these
structured fields with explicit syntax for this linear-
white-space, the existence of another "lexical" analyzer is
assumed. This analyzer does not apply for field bodies which
are simply unstructured strings of text, as described above.
It provides an interpretation of the unfolded text comprising
the body of the field as a sequence of lexical symbols.
These symbols are:
- individual special characters
- quoted-strings
Standard for the Format of Text Messages 8
III. Syntax
B. Lexical Analysis
- comments
- atoms
The first three of these symbols are self-delimiting. Atoms
are not; they therefore are delimited by the self-delimiting
symbols and by linear-white-space. For the purposes of re-
generating sequences of atoms and quoted-strings, exactly one
SPACE is assumed to exist and should be used between them.
(Also, in Section III.B.3.a, note the rules concerning
treatment of multiple continguous LWSP-chars.)
So, for example, the folded body of an address field
":sysmail"@ Some-Host,
Muhammed(I am the greatest)Ali at(the)WBA
is analyzed into the following lexical symbols and types:
":sysmail" quoted string
@ special
Some-Host atom
, special
Muhammed atom
(I am the greatest) comment
Ali atom
at atom
(the) comment
WBA atom
The cononical representations for the data in these addresses
are the following strings (note that there is exactly one
SPACE between words):
:sysmail at Some-Host
and
Muhammed Ali at WBA
2. Formal Definitions
The first four rules, below, indicate a meta-syntax for fields,
without regard to their particular type or internal syntax. The
remaining rules define basic syntactic structures which are used
by the rules in Sections III.C, III.D, and III.E.
field = field-name ":" [ field-body ] CRLF
field-name = fnatom *( LWSP-char [fnatom] )
Standard for the Format of Text Messages 9
III. Syntax
B. Lexical Analysis
fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">
field-body = field-body-contents
[CRLF LWSP-char field-body]
field-body-contents = <the TELNET ASCII characters making up the
field-body, as defined in the following sections,
and consisting of combinations of atom, quoted-
string, and specials tokens, or else consisting of
texts>
; ( Octal, Decimal.)
CHAR = <any TELNET ASCII character> ; ( 0-177, 0.-127.)
ALPHA = <any TELNET ASCII alphabetic character>
; (101-132, 65.- 90.)
; (141-172, 97.-122.)
DIGIT = <any TELNET ASCII digit> ; ( 60- 71, 48.- 57.)
CTL = <any TELNET ASCII control ; ( 0- 37, 0.- 31.)
character and DEL> ; ( 177, 127.)
CR = <TELNET ASCII carriage return>;( 15, 13.)
LF = <TELNET ASCII linefeed> ; ( 12, 10.)
SPACE = <TELNET ASCII space> ; ( 40, 32.)
HTAB = <TELNET ASCII horizontal-tab>; ( 11, 9.)
<"> = <TELNET ASCII quote mark> ; ( 42, 34.)
CRLF = CR LF
LWSP-char = SPACE / HTAB ; semantics = SPACE
linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE
; CRLF => folding
specials = "(" / ")" / "<" / ">" / "@" ; To use in a word,
/ "," / ";" / ":" / "\" / <"> ; word must be a
; quoted-string.
delimiters = specials / comment / linear-white-space
text = <any CHAR, including bare ; => atoms, specials,
CR and/or bare LF, but NOT ; comments and
including CRLF> ; quoted-strings are
; NOT interpreted.
atom = 1*<any CHAR except specials and CTLs>
quoted-string = <"> *(qtext/quoted-pair) <">; Any number of qtext
; chars or any
; quoted char.
qtext = <any CHAR excepting <"> ; => may be folded
and CR, and including
linear-white-space>
Standard for the Format of Text Messages 10
III. Syntax
B. Lexical Analysis
comment = "(" *(ctext / comment / quoted-pair) ")"
ctext = <any CHAR excluding "(", ; => may be folded
")" and CR, and including
linear-white-space>
quoted-pair = "\" CHAR
3. Clarifications
a. "White space"
Remember that in field-names and structured field bodies,
MULTIPLE LINEAR WHITE SPACE TELNET ASCII CHARACTERS (namely
HTABs and SPACEs) ARE TREATED AS SINGLE SPACES AND MAY FREELY
SURROUND ANY SYMBOL. In all header fields, the only place in
which at least one space is REQUIRED is at the beginning of
continuation lines in a folded field. When passing text to
processes which do not interpret text according to this
standard (e.g., ARPANET FTP mail servers), then exactly one
SPACE should be used in place of arbitrary linear-white-space
and comment sequences.
WHEREVER A MEMBER OF THE LIST OF <DELIMITER>S IS ALLOWED,
LWSP-CHARS MAY ALSO OCCUR BEFORE AND/OR AFTER IT.
Writers of mail-sending (i.e. header generating) programs
should realize that there is no Network-wide definition of
the effect of horizontal-tab TELNET ASCII characters on the
appearance of text at another Network host; therefore, the
use of tabs in message headers, though permitted, is
discouraged.
Note that during transmissions across the ARPANET using
TELNET NVT connections, data must conform to TELNET NVT
conventions (e.g., CR must be followed by either LF, making a
CRLF, or <null>, if the CR is to stand alone).
b. Comments
Comments are detected as such only within field-bodies of
structured fields. A comment is a set of TELNET ASCII
characters, which is not within a quoted-string and which is
enclosed in matching parentheses; parentheses nest, so that
if an unquoted left parenthesis occurs in a comment string,
there must also be a matching right parenthesis. When a
comment is used to act as the delimiter between a sequence of
two lexical symbols, such as two atoms, it is lexically
equivalent with one SPACE, for the purposes of regenerating
the sequence, such as when passing the sequence onto an FTP
mail server.
Standard for the Format of Text Messages 11
III. Syntax
B. Lexical Analysis
In particular comments are NOT passed to the FTP server, as
part of a MAIL or MLFL command, since comments are not part
of the "formal" address.
If a comment is to be "folded" onto multiple lines, then the
syntax for folding must be adhered to. (See items III.B.1.a,
above, and III.B.3.f, below.) Note that the official
semantics therefore do not "see" any unquoted CRLFs which are
in comments, although particular parsing programs may wish to
note their presence. For these programs, it would be
reasonable to interpret a "CRLF LWSP-char" as being a CRLF
which is part of the comment; i.e., the CRLF is kept and the
LWSP-char is discarded. Quoted CRLFs (i.e., a backslash
followed by a CR followed by a LF) still must be followed by
at least one LWSP-char.
c. Delimiting and quoting characters
The quote character (backslash) and characters which delimit
syntactic units are not, generally, to be taken as data which
are part of the delimited or quoted unit(s). The one
exception is SPACE. In particular, the quotation-marks which
define a quoted-string, the parentheses which define a
comment and the backslash which quotes a following character
are NOT part of the quoted-string, comment or quoted
character. A quotation-mark which is to be part of a
quoted-string, a parenthesis which is to be part of a comment
and a backslash which is to be part of either must each be
preceded by the quote-character backslash ("\"). Note that
the syntax allows any character to be quoted within a
quoted-string or comment; however only certain characters
MUST be quoted to be included as data. These characters are
those which are not part of the alternate text group (i.e.,
ctext or qtext).
A single SPACE is assumed to exist between contiguous words
in a phrase, and this interpretation is independent of the
actual number of LWSP-chars which the creator places between
the words. To include more than one SPACE, the creator must
make the LWSP-chars be part of a quoted-string.
Quotation marks which delimit a quoted string and backslashes
which quote the following character should NOT accompany the
quoted-string when the string is used with processes that do
not interpret data according to this specification (e.g.,
ARPANET FTP mail servers).
Standard for the Format of Text Messages 12
III. Syntax
B. Lexical Analysis
d. Quoted-strings
Where permitted (i.e., in words in structured fields)
quoted-strings are treated as a single symbol (i.e.
equivalent to an atom, syntactically). If a quoted-string is
to be "folded" onto multiple lines, then the syntax for
folding must be adhered to. (See items III.B.1.a, above, and
III.B.3.f, below.) Note that the official semantics
therefore do not "see" any bare CRLFs which are in quoted-
strings, although particular parsing programs may wish to
note their presence. For these programs, it would be
reasonable to interpret a "CRLF LWSP-char" as being a CRLF
which is part of the quoted-string; i.e., the CRLF is kept
and the LWSP-char is discarded. Quoted CRLFs (i.e., a
backslash followed by a CR followed by a LF) are also subject
to rules of folding, but the presence of the quoting
character (backslash) explicitly indicates that the CRLF is
data to the quoted string. Stripping off the first following
LWSP-char is also appropriate when parsing quoted CRLFs.
e. Bracketing characters
There are three types of brackets which must be well nested:
o Parentheses are used to indicate comments.
o Angle brackets ("<" and ">") are generally used
to indicate the presence of at least one machine-
usable code (e.g., delimiting mailboxes).
o Colon/semi-colon (":" and ";") are used in
address specifications to indicate that the
included list of addresses are to be treated as a
group.
f. Case independence of certain specials atoms
Certain atoms, which are represented in the syntax as literal
alphabetic strings, can be represented in any combination of
upper and lower case. These are:
- field-name,
- "Include", "Postal" and equivalent atoms in a
":"<atom>":" address specification,
- "at", in a host-indicator,
- node,
- day-of-week,
- month, and
- zones.
When matching an atom against one of these literals, case is
to be ignored. For example, the field-names "From", "FROM",
Standard for the Format of Text Messages 13
III. Syntax
B. Lexical Analysis
"from", and even "FroM" should all be treated identically.
However, the case shown in this specification is suggested
for message-creating processes. Note that, at the level of
this specification, case IS relevant to other words and
texts. Also see Section IV.A.1.f, below.
g. Folding long lines
Each header item (field of the message) may be represented on
exactly one line consisting of the name of the field and its
body; this is what the parser sees. For readability, it is
recommended that the field-body portion of long header items
be "folded" onto multiple lines of the actual header. "Long"
is commonly interpreted to mean greater than 65 or 72
characters. The former length is recommended as a limit, but
it is not imposed by this standard.
h. Backspace characters
Backspace TELNET ASCII characters (ASCII BS, decimal 8.) may
be included in texts and quoted-strings to effect
overstriking; however, any use of backspaces which effects an
overstrike to the left of the beginning of the text or
quoted-string is prohibited.
C. GENERAL SYNTAX OF MESSAGES:
NOTE: Due to an artifact of the notational conventions,
the syntax indicates that, when present, "Date",
"From", "Sender", and "Reply-To" fields must be
in a particular order. These header items must
be unique (occur exactly once). However header
fields, in fact, are NOT required to occur in any
particular order, except that the message body
must occur AFTER the headers. For readability
and ease of parsing by simple systems, it is
recommended that headers be sent in the order
"Date", "From", "Subject", "Sender", "To", "cc",
etc. This specification permits multiple
occurrences of most optional-fields. However,
their interpretation is not specified here, and
their use is strongly discouraged.
The following syntax for the bodies of various fields should be
thought of as describing each field body as a single long string
(or line). The section on Lexical Analysis (section II.B)
indicates how such long strings can be represented on more than
one line in the actual transmitted message.
Standard for the Format of Text Messages 14
III. Syntax
C. Messages
message = fields *( CRLF *text ) ; Everything after
; first null line
; is message body
fields = date-field ; Creation time-stamp
originator-fields ; & author id are
*optional-field ; required: others
; are all optional
originator-fields =
( "From" ":" mailbox ; Single author
["Reply-To" ":" #address] )
/ ( "From" ":" 1#address ; Multiple authors &
"Sender" ":" mailbox ; may have non-mach-
["Reply-To" ":" #address] ); ine addresses
date-field = "Date" ":" date-time
optional-field =
"To" ":" #address
/ "cc" ":" #address
/ "bcc" ":" #address ; Blind carbon
/ "Subject" ":" *text
/ "Comments" ":" *text
/ "Message-ID" ":" mach-id ; Only one allowed
/ "In-Reply-To"":" #(phrase / mach-id)
/ "References" ":" #(phrase / mach-id)
/ "Keywords" ":" #phrase
/ extension-field ; To be defined in
; supplemental
; specifications
/ user-defined-field ; Must have unique
; field-name & may
; be pre-empted
extension-field = <Any field which is defined in a document
published as a formal extension to this
specification>
user-defined-field = <Any field which has not been defined in
this specification or published as an extension to
this specification; names for such fields must be
unique and may be preempted by published
extensions>
Standard for the Format of Text Messages 15
III. Syntax
D. Addressee Items
D. SYNTAX OF GENERAL ADDRESSEE ITEMS
address = host-phrase ; Machine mailbox
/ ( [phrase] "<" #address ">") ; Individual / List
/ ( [phrase] ":" #address ";") ; Group
/ quoted-string ; Arbitrary text
/ (":" ( "Include" ; File, w/ addr list
/ "Postal" ; (U.S.) Postal addr
/ atom ) ; Extended data type
":" address)
mailbox = host-phrase / (phrase mach-id)
mach-id = "<" host-phrase ">" ; Contents must never
; be modified!
E. SUPPORTING CONSTRUCTS
host-phrase = phrase host-indicator ; Basic address
host-indicator = 1*( ("at" / "@") node ) ; Right-most node is
; at top of network
; hierarchy; left-
; most must be host
node = word / 1*DIGIT ; Official host or
; network name or
; decimal address
date-time = [ day-of-week "," ] date time
day-of-week = "Monday" / "Mon" / "Tuesday" / "Tue"
/ "Wednesday" / "Wed" / "Thursday" / "Thu"
/ "Friday" / "Fri" / "Saturday" / "Sat"
/ "Sunday" / "Sun"
date = 1*2DIGIT ["-"] month ; day month year
["-"] (2DIGIT /4DIGIT) ; e.g. 20 Aug [19]77
month = "January" / "Jan" / "February" / "Feb"
/ "March" / "Mar" / "April" / "Apr"
/ "May" / "June" / "Jun"
/ "July" / "Jul" / "August" / "Aug"
/ "September" / "Sep" / "October" / "Oct"
/ "November" / "Nov" / "December" / "Dec"
Standard for the Format of Text Messages 16
III. Syntax
E. Supporting Constructs
time = hour zone ; ANSI and Military
; (seconds optional)
hour = 2DIGIT [":"] 2DIGIT [ [":"] 2DIGIT ]
; 0000[00] - 2359[59]
zone = ( ["-"] ( "GMT" ; Relative to GMT:
; North American
/ "NST" / ; Newfoundland:-3:30
/ "AST" / "ADT" ; Atlantic: - 4/ - 3
/ "EST" / "EDT" ; Eastern: - 5/ - 4
/ "CST" / "CDT" ; Central: - 6/ - 5
/ "MST" / "MDT" ; Mountain: - 7/ - 6
/ "PST" / "PDT" ; Pacific: - 8/ - 7
/ "YST" / "YDT" ; Yukon: - 9/ - 8
/ "HST" / "HDT" ; Haw/Ala -10/ - 9
/ "BST" / "BDT" ; Bering: -11/ -10
1ALPHA )) ; Military: Z = GMT;
; A:-1; (J not used)
; M:-12; N:+1; Y:+12
/ ( ("+" / "-") 4DIGIT ) ; Local differential
; hours/min. (HHMM)
phrase = 1*word ; Sequence of words.
; Separation seman-
; tically = SPACE
word = atom / quoted-string
Standard for the Format of Text Messages 17
IV. Semantics
A. Address Fields
IV. SEMANTICS
A. ADDRESS FIELDS
1. General
a. The phrase part of a host-phrase in an address specification
(i.e., the host's name for the mailbox) is understood to be
whatever the receiving FTP Server allows (for example, TENEX
systems do not now understand addresses of the form "P. D.
Q. Bach", but another system might).
Note that a mailbox is a conceptual entity which does not
necessarily pertain to file storage. For example, some sites
may choose to print mail on their line printer and deliver
the output to the addressee's desk.
An individual may have several mailboxes and a group of
individuals may wish to receive mail as a single unit (i.e.,
a distribution list). The second and third alternatives of
an address list (#address) allow naming a collection of
subordinate addresses list(s). Recipient mailboxes are
specified within the bracketed part ("<" - ">" or ":" - ";")
of such named lists. The use of angle-brackets ("<", ">") is
intended for the cases of individuals with multiple mailboxes
and of special mailbox lists; it is not expected to be nested
more than one level, although the specification allows such
nesting. The use of colon/semi-colon (":", ";") is intended
for the case of groups. Groups can be expected to nest
(i.e., to contain subgroups). For both individuals and
groups, a copy of the transmitted message is to be sent to
EACH mailbox listed. For the case of a special list,
treatment of addresses is defined in the relevant subsections
of this section.
b. The inclusion of bare quoted-strings as addresses (i.e., the
fourth address-form alternative) is allowed as a syntactic
convenience, but no semantics are defined for their use.
However, it is reasonable, when replicating an address list,
to replicate ALL of its members, including quoted-strings.
c. ":Include:" specifications are used to refer to one or more
locations containing stored address lists (#address). If
more than one location is referenced, the address part of the
Include phrase must be a list (#address) surrounded by
angle-brackets, as per the "Individual / List" alternative of
<address>. Constituent addresses must resolve to a host-
Standard for the Format of Text Messages 18
IV. Semantics
A. Address Fields
phrase; only they have any meaning within this construct.
The phrase part of indicated host-phrases should contain text
which the referenced host can resolve to a file. This
standard is not a protocol and so does not prescribe HOW data
is to be retrieved from the file. However, the following
requirements are made:
o The file must be accessible through the local
operating system interface (if it exists), given
adequate user access rights; and
o If a host has an FTP server and a user is able
to retrieve any files from the host using that
server, then the file must be accessible through
FTP, using DEFAULT transfer settings, given
adequate user access rights.
It is intended that this mechanism allow programs to retrieve
such lists automatically.
The interpretation of such a file reference follows. This is
not intended to imply any particular implementation scheme,
but is presented to aid in understanding the notion of
including file contents in address lists:
o Elements of the address list part are alternates
and the contents of ONLY ONE of them are to be
included in the resultant address list.
o The contents of the file indicated by a member
host-phrase are treated as an address list and
are inserted as an address list (#address) in
the position of the path item in the syntax.
That is, the TELNET ASCII characters specifying
the entire Include <address> is replaced by the
contents of one of the files to which the host-
phrase(s), of the address list (#address),
refers. Therefore, the contents of each file,
indicated by an Include address, must be
syntactically self-contained and must adhere to
the full syntax prescribed herein for an address
list.
d. ":Postal:" specifications are used to indicate (U.S.) postal
addresses, but can be treated the same as quoted-string
addresses. To reference a list of postal addresses, the list
must conform to the "Individual / List" alternative of
<address>. The ":Include:" alternative also is valid.
e. The "':' atom ':'" syntax is intended as a general mechanism
for indicating specially data-typed addresses. As with
extension-fields, the authors of this document will regulate
Standard for the Format of Text Messages 19
IV. Semantics
A. Address Fields
the publishing of specifications for these extended data-
types. In the absence of defined semantics, any occurrence
of an address in this form may be treated as a quoted-string
address.
f. A node name must be THE official name of a network or a host,
or else a decimal number indicating the Network address for
that network or host, at the time the message is created.
The USE OF NUMBERS IS STRONGLY DISCOURAGED and is permitted
only due to the occasional necessity of bypassing local name
tables. For the ARPANET, official names are maintained by
the Network Information Center at SRI International, Menlo
Park, California.
Whenever a message might be transmitted or migrate to a host
on another network, full hierarchical addresses must be
specified. These are indicated as a series of words,
separated by at-sign or "at" indications. The communication
environment is assumed to consist of a collection of networks
organized as independent "trees" except for connections
between the root nodes. That is, only the roots can act as
gateways between these independent networks. While other
actual connections may exist, it is believed that presuming
this type of organization will provide a reliable method for
describing VALID, if not EFFICIENT, paths between hosts. A
typical full mailbox specification might therefore look like:
Friendly User @ hosta @ local-net1 @ major-netq
In the simplest case, a mail-sending host should transmit the
message to the node which is mentioned last (farthest to the
right), strip off that node reference from the specification,
and then pass the remaining host-phrase to the recipient host
(in the ARPANET, its FTP server) for it to process. This
treats the remaining portion of the host-indicator merely as
the terminating part of the phrase.
NOTE: When passing any portion of a host-indicator
onto a process which does not interpret data
according to this standard (e.g., ARPANET
FTP servers), "@" must be used and not "at"
and it must not be preceded or followed by
any LWSP-chars. Using the above example,
the following string would be passed to the
major-netq gateway:
Friendly User@hosta@local-net1
When the sending host has more knowledge of the network
environment, then it should send the message along a more
efficient path, making appropriate changes to the form of the
host-phrase which it gives to the recipient host.
Standard for the Format of Text Messages 20
IV. Semantics
A. Address Fields
To use the above specification as an example: If a sending
hostb also were part of local-net1, then it could send the
message directly to hosta and would give only the phrase
"Friendly User" to hosta's mail-receiving program. If hostb
were part of local-net2, along with hostc, and happened to
know that hosta and hostc were part of another local-net,
then hostb could send the message to hostc to the address
"Friendly User@hosta".
The phrase in a host-phrase is intended to be meaningful only
to the indicated receiving host. To all other hosts, the
phrase is to be treated as an uninterpreted string. No case
transformations should be (automatically) performed on the
phrase. The phrase is passed to the local host's mail
sending program; it is the responsibility of the destination
host's mail receiving (distribution) program to perform case
mapping on this phrase, if required, to deliver the mail.
2. Originator Fields
WARNING: The standard allows only a subset of the
combinations possible with the From, Sender,
and Reply-To fields. The limitation is
intentional.
a. From
This field contains the identity of the person(s) who wished
this message to be sent. The message-creation process should
default this field to be a single machine address, indicating
the AGENT (person or process) entering the message. If this
is NOT done, the "Sender" field MUST be present; if this IS
done, the "Sender" field is optional.
b. Sender
This field contains the identity of the AGENT (person or
process) who sends the message. It is intended for use when
the sender is not the author of the message, or to indicate
who among a group of authors actually sent the message. If
the contents of the "Sender" field would be completely
redundant with the "From" field, then the "Sender" field need
not be present and its use is discouraged (though still
legal); in particular, the "Sender" field MUST be present
if it is NOT the same as the "From" Field.
The Sender host-phrase includes a phrase which must
correspond to a specific agent (i.e., a human user or a
computer program) rather than a standard address. This
indicates the expectation that the field will identify the
single AGENT (person or process) responsible for sending the
Standard for the Format of Text Messages 21
IV. Semantics
A. Address Fields
mail and not simply include the name of a mailbox from which
the mail was sent. For example in the case of a shared login
name, the name, by itself, would not be adequate. The phrase
part of the host-phrase, which refers to this agent, is
expected to be a computer system term, and not (for example)
a generalized person reference which can be used outside the
network text message context.
Since the critical function served by the "Sender" field is
the identification of the agent responsible for sending mail
and since computer programs cannot be held accountable for
their behavior, is strongly recommended that when a computer
program generates a message, the HUMAN who is responsible for
that program be referenced as part of the "Sender" field
host-phrase.
c. Reply-To
This field provides a general mechanism for indicating any
mailbox(es) to which responses are to be sent. Three typical
uses for this feature can be distinguished. In the first
case, the author(s) may not have regular machine-based
mailboxes and therefore wish(es) to indicate an alternate
machine address. In the second case, an author may wish
additional persons to be made aware of, or responsible for,
responses; responders should send their replies to the
"Reply-To" mailbox(es) listed in the original message. A
somewhat different use may be of some help to "text message
teleconferencing" groups equipped with automatic distribution
services: include the address of that service in the
"Reply-To" field of all messages submitted to the
teleconference; then participants can "reply" to conference
submissions to guarantee the correct distribution of any
submission of their own.
Reply-To fields are NOT required to contain any machine
addresses (i.e., host-phrases). Note, however, that the
absence of even one valid network address will tend to
prevent software systems from automatically assisting users
in conveniently responding to mail.
NOTE: For systems which automatically generate address lists for
replies to messages, the following recommendations are made:
o The receiver, when replying to a message, should
NEVER automatically include the "Sender" host-phrase
in the reply's address list;
o If the "Reply-To" field exists, then the reply
should go ONLY to the addresses indicated in that
field and not to the addresses indicated in the
"From" field.
Standard for the Format of Text Messages 22
IV. Semantics
A. Address Fields
(Extensive examples are provided in Section V.) This
recommendation is intended only for originator-fields and is not
intended to suggest that replies should not also be sent to the
other recipients of this message. It is up to the respective
mail handling programs to decide what additional facilities will
be provided.
3. Receiver Fields
a. To
This field contains the identity of the primary recipients of
the message.
b. cc
This field contains the identity of the secondary recipients
of the message.
b. Bcc
This field contains the identity of additional recipients of
the message. The contents of this field are not included in
copies of the message sent to the primary and secondary
recipients. Some systems may choose to include the text of
the "Bcc" field only in the author(s)'s copy, while others
may also include it in the text sent to all those indicated
in the "Bcc" list.
B. REFERENCE SPECIFICATION FIELDS
1. Message-ID
This field contains a unique identifier (the phrase) which refers
to THIS version of THIS message. The uniqueness of the message
identifier is guaranteed by the host which generates it. This
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 should each receive a new message identifier.
2. In-Reply-To
The contents of this field identify previous correspondence which
this message answers. Note that if message identifiers are used
in this field, they must use the mach-id specification format.
Standard for the Format of Text Messages 23
IV. Semantics
B. Reference Specification Fields
3. References
The contents of this field identify other correspondence which
this message references. Note that if message identifiers
are used, they must use the mach-id specification format.
4. Keywords
This field contains keywords or phrases, separated by commas.
C. OTHER FIELDS AND SYNTACTIC ITEMS
1. Subject
The "Subject" field is intended to provide as much information as
necessary to adequately summarize or indicate the nature of the
message.
2. Comments
Permits adding text comments onto the message without disturbing
the contents of the message's body.
3. Extension-field
A relatively limited number of common fields have been defined in
this document. As network mail requirements dictate, additional
fields may be standardized. The authors of this document will
regulate the publishing of such definitions as extensions to the
basic specification.
4. User-defined-field
Individual users of network mail are free to define and use
additional header fields. Such fields must have names which are
not already used in the current specification or in any
definitions of extension-fields, and the overall syntax of these
user-defined-fields must conform to this specification's rules
for delimiting and folding fields. Due to the extension-field
publishing process, the name of a user-defined-field may be pre-
empted.
Standard for the Format of Text Messages 24
IV. Semantics
D. Dates
D. DATES AND TIMES
If included, day-of-week must be the day implied by the date
specification.
Time zone may be indicated in several ways. The military
standard uses a single character for each zone. "Z" is
Greenwhich Mean Time; "A" indicates one hour earlier, and "M"
indicates 12 hours earlier; "N" is one hour later, and "Y" is 12
hours later. The letter "J" is not used. The other remaining
two forms are taken from ANSI standard X3.51-1975. One allows
explicit indication of the amount of offset from GMT; the other
uses common 3-character strings for indicating time zones in
North America.
Standard for the Format of Text Messages 25
V. Examples
A. Addresses
V. EXAMPLES
A. ADDRESSES
1. Alfred E. Neuman <Neuman at BBN-TENEXA>
2. Neuman@BBN-TENEXA
These two "Alfred E. Neuman" examples have identical semantics,
as far as the operation of the local host's mail sending
(distribution) program (also sometimes called its "mailer") and
the remote host's FTP server are concerned. In the first
example, the "Alfred E. Neuman" is ignored by the mailer, as
"Neuman at BBN-TENEXA" completely specifies the recipient. The
second example contains no superfluous information, and, again,
"Neuman@BBN-TENEXA" is the intended recipient.
3. Al Neuman at BBN-TENEXA
This is identical to "Al Neuman <Al Neuman at BBN-TENEXA>". That
is, the full phrase, "Al Neuman", is passed to the FTP server.
Note that not all FTP servers accept multi-word identifiers; and
some that do accept them will treat each word as a different
addressee (in this case, attempting to send a copy of the message
to "Al" and a copy to "Neuman").
4. "George Lovell, Ted Hackle" <Shared-Mailbox at Office-1>
This form might be used to indicate that a single mailbox is
shared by several users. The quoted string is ignored by the
originating host's mailer, as "Shared-Mailbox at Office-1"
completely specifies the destination mailbox.
4. Wilt (the Stilt) Chamberlain at NBA
The "(the Stilt)" is a comment, which is NOT included in the
destination mailbox address handed to the originating system's
mailer. The address is the string "Wilt Chamberlain", with
exactly one space between the first and second words. (The
quotation marks are not included.)
Standard for the Format of Text Messages 26
V. Examples
B. Address Lists
B. ADDRESS LISTS
Gourmets: Pompous Person <WhoZiWhatZit at Cordon-Bleu>,
Cooks: Childs at WGBH, Galloping Gourmet at
ANT (Australian National Television);,
Wine Lovers: Cheapie at Discount-Liquors,
Port at Portugal;;,
Jones at SEA
This group list example points out the use of comments, the
nesting of groups, and the mixing of addresses and groups. Note
that the two consecutive semi-colons preceding "Jones at SEA"
mean that Jones is NOT a member of the Gourmets group.
C. ORIGINATOR ITEMS
1. Author-sent
George Jones logs into his Host as "Jones". He sends mail
himself.
From: Jones at Host
or
From: George Jones <Jones at Host>
2. Secretary-sent
George Jones logs in as Jones on his Host. His secretary, who
logs in as Secy on Shost sends mail for him. Replies to the mail
should go to George, of course.
From: George Jones <Jones at Host>
Sender: Secy at SHost
3. Shared directory or unrepresentative directory-name
George Jones logs in as Group at Host. He sends mail himself;
replies should go to the Group mailbox.
From: George Jones <Group at Host>
Standard for the Format of Text Messages 27
V. Examples
C. Originator Items
4. Secretary-sent, for user of shared directory
George Jones' secretary sends mail for George in his capacity as
a member of Group while logged in as Secy at Host. Replies
should go to Group.
From: George Jones<Group at Host>
Sender: Secy at Host
Note that there need not be a space between "Jones" and the "<",
but adding a space enhances readability (as is the case in other
examples).
5. Secretary acting as full agent of author
George Jones asks his secretary (Secy at Host) to send a message
for him in his capacity as Group. He wants his secretary to
handle all replies.
From: George Jones <Group at Host>
Sender: Secy at Host
Reply-To: Secy at Host
6. Agent for user without online mailbox
A non-ARPANET user friend of George's, Sarah, is visting.
George's secretary sends some mail to a friend of Sarah in
computer-land. Replies should go to George, whose mailbox is
Jones at Host.
From: Sarah Friendly
Sender: Secy at Host
Reply-To: Jones at Host
7. Sent by member of a committee
George is a member of a committee. He wishes to have any replies
to his message go to all committee members.
From: George Jones
Sender: Jones at Host
Reply-To: Big-committee: Jones at Host,
Smith at Other-Host,
Doe at Somewhere-Else;
Note that if George had not included himself in the enumeration
of Big-committee, he would not have gotten an implicit reply; the
presence of the "Reply-to" field SUPERSEDES the sending of a
reply to the person named in the "From" field.
Standard for the Format of Text Messages 28
V. Examples
C. Originator Items
8. Example of INCORRECT use
George desires a reply to go to his secretary; therefore his
secretary leaves his mailbox address off the "From" field,
leaving only his name, which is not, itself, a mailbox address.
From: George Jones
Sender: Secy at SHost
THIS IS NOT PERMITTED. Replies are NEVER implicitly sent to the
"Sender"; George's secretary should have used the "Reply-To"
field, or the mail creating program should have forced the
secretary to.
9. Agent for member of a committee
George's secretary sends out a message which was authored jointly
by all the members of the "Big-committee".
From: Big-committee: Jones at Host,
Smith at Other-Host,
Doe at Somewhere-Else;
Sender: Secy at SHost
D. COMPLETE HEADERS
1. Minimum required:
Date: 26 August 1976 1429-EDT
From: Jones at Host
2. Using some of the additional fields:
Date: 26 August 1976 1430-EDT
From:George Jones<Group at Host>
Sender:Secy at SHOST
To:Al Neuman at Mad-Host,
Sam Irving at Other-Host
Message-ID: <some string at SHOST>
Standard for the Format of Text Messages 29
V. Examples
D. Complete Headers
3. About as complex as you're going to get:
Date : 27 Aug 1976 0932-PDT
From : Ken Davis <KDavis at Other-Host>
Subject : Re: The Syntax in the RFC
Sender : KSecy at Other-Host
Reply-To : Sam Irving at Other-Host
To : George Jones <Group at Host>,
Al Neuman at Mad-Host
cc : Important folk:
Tom Softwood <Balsa at Another-Host>,
Sam Irving at Other-Host;,
Standard Distribution::Include:
</main/davis/people/standard at Other-Host,
"<Jones>standard.dist.3" at Tops-20-Host>,
(The following Included Postal list is part
of Standard Distribution.)
:Postal::Include: Non-net-addrs@Other-host;,
:Postal: "Sam Irving, P.O. Box 001, Las Vegas,
Nevada" (So that he can stay
apprised of the situation)
Comment : Sam is away on business. He asked me to handle
his mail for him. He'll be able to provide a
more accurate explanation when he returns
next week.
In-Reply-To: <some string at SHOST>
Special (action): This is a sample of multi-word field-
names, using a range of characters. There
could also be a field-name "Special (info)".
Message-ID: <4231.629.XYzi-What at Other-Host>
Standard for the Format of Text Messages 31
Appendix
A. Alphabetical Listing of Syntax Rules
APPENDIX
A. ALPHABETICAL LISTING OF SYNTAX RULES
address = host-phrase / quoted-string
/ (*phrase "<" #address ">" )
/ (*phrase ":" #address ";" )
/ (":" ("Include" / "Postal" / atom) ":" address)
ALPHA = <any TELNET ASCII alphabetic character>
atom = 1*<any CHAR except specials and CTLs>
CHAR = <any TELNET ASCII character>
comment = "(" *(ctext / comment / quoted-pair) ")"
CR = <TELNET ASCII carriage return>
CRLF = CR LF
ctext = <any CHAR excluding "(", ")", CR, LF and
including linear-white-space>
CTL = <any TELNET ASCII control character and DEL>
date = 1*2DIGIT ["-"] month ["-"] (2DIGIT /4DIGIT)
date-field = "Date" ":" date-time
date-time = [ day-of-week "," ] date time
day-of-week = "Monday" / "Mon" / "Tuesday" / "Tue"
/ "Wednesday" / "Wed" / "Thursday" / "Thu"
/ "Friday" / "Fri" / "Saturday" / "Sat"
/ "Sunday" / "Sun"
delimiters = specials / comment / linear-white-space
DIGIT = <any TELNET ASCII digit>
extension-field = <Any field which is defined in a document
published as a formal extension to this
specification>
field = field-name ":" [ field-body ] CRLF
fields = date-field originator-fields *optional-field
field-body = field-body-contents
[CRLF LWSP-char field-body]
field-body-contents = <the TELNET ASCII characters making up the
field-body, as defined in the following sections,
and consisting of combinations of atom, quoted-
string, and specials tokens, or else consisting of
texts>
field-name = fnatom *(LWSP-char [fnatom])
fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">
Standard for the Format of Text Messages 32
Appendix
A. Alphabetical Listing of Syntax Rules
host-indicator = 1*( ("at" / "@") node )
host-phrase = phrase host-indicator
hour = 2DIGIT [":"] 2DIGIT [ [":"] 2DIGIT ]
HTAB = <TELNET ASCII horizontal-tab>
LF = <TELNET ASCII linefeed>
linear-white-space = 1*([CRLF] LWSP-char)
LWSP-char = SPACE / HTAB
mach-id = "<" host-phrase ">"
mailbox = host-phrase / (phrase mach-id)
message = fields *(CRLF *text)
month = "January" / "Jan" / "February" / "Feb"
/ "March" / "Mar" / "April" / "Apr"
/ "May" / "June" / "Jun"
/ "July" / "Jul" / "August" / "Aug"
/ "September" / "Sep" / "October" / "Oct"
/ "November" / "Nov" / "December" / "Dec"
node = word / 1*DIGIT
optional-field =
"To" ":" #address
/ "cc" ":" #address
/ "bcc" ":" #address
/ "Subject" ":" *text
/ "Comments" ":" *text
/ "Message-ID" ":" mach-id
/ "In-Reply-To"":" #(phrase / mach-id)
/ "References" ":" #(phrase / mach-id)
/ "Keywords" ":" #phrase
/ extension-field
/ user-defined-field
originator-fields =
( "From" ":" mailbox
["Reply-To" ":" #address] )
/ ( "From" ":" 1#address
"Sender" ":" mailbox
["Reply-To" ":" #address] )
phrase = 1*word
quoted-pair = "\" CHAR
quoted-string = <"> *(qtext / quoted-pair) <">
qtext = <any CHAR except <">, CR, or LF and including
linear-white-space>
SPACE = <TELNET ASCII space>
specials = "(" / ")" / "<" / ">" / "@"/ "," / ";" / ":"
/ "\" / <">
text = <any CHAR, including bare CR and/or bare LF, but
NOT including CRLF>
Standard for the Format of Text Messages 33
Appendix
A. Alphabetical Listing of Syntax Rules
time = hour zone
user-defined-field = <Any field which has not been defined in
this specification or published as an extension to
this specification; names for such fields must be
unique and may be preempted by putlished
extensions>
word = atom / quoted-string
zone = ( ("+" / "-") 4DIGIT )
/ ( ["-"] (1ALPHA
/ "GMT" / "NST" / "AST" / "ADT" / "EST" / "EDT"
/ "CST" / "CDT" / "MST" / "MDT" / "PST" / "PDT"
/ "YST" / "YDT" / "HST" / "HDT" / "BST" / "BDT" ))
<"> = <TELNET ASCII quote mark>
Standard for the Format of Text Messages 35
Appendix
B. Simple Parsing
B. SIMPLE PARSING
Some mail-reading software systems may wish to perform only
minimal processing, ignoring the internal syntax of structured
field-bodies and treating them the same as unstructured-field-
bodies. Such software will need only to distinguish:
- Header fields from the message body,
- Beginnings of fields from lines which continue fields,
- Field-names from field-contents.
The abbreviated set of syntactic rules which follows will
suffice for this purpose. They describe a limited view of
messages and are a subset of the syntactic rules provided in the
main part of this specification. One small exception is that the
contents of field-bodies consist only of text:
SYNTAX:
message = *field *(CRLF *text)
field = field-name ":" [field-body] CRLF
field-name = fnatom *( LWSP-char [fnatom] )
fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">
field-body = *text [CRLF LWSP-char field-body]
SEMANTICS:
Headers occur before the message body and are terminated by
a null line (i.e., two contiguous CRLFs).
A line which continues a header field begins with a SPACE or
HTAB character, while a line beginning a field starts with a
printable character which is not a colon.
A field-name consists of one or more printable characters
(excluding colon), each separated by one or more SPACES or HTABS.
A field-name MUST be contained on one line. Upper and lower case
are not distinguished when comparing field-names.
Standard for the Format of Text Messages 37
Bibliography
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