NIC # 41952
Obsoletes: RFC #561
RFC #680 (NIC #32116)
RFC #724 (NIC #37435)
ARPA NETWORK TEXT MESSAGES(1)
21 November 1977
David H. Crocker
The Rand Corporation
John J. Vittal
Bolt Beranek and Newman Inc.
Kenneth T. Pogran
Massachusets Institute of Technology
_________________________________________________________________(1)This work was supported by the Defense Advanced Research
(2)The authors' postal addresses are: D. Crocker, The Rand
ARPA's Committee on Computer-Aided Human Communication(CAHCOM) wishes to promulgate a standard for the format of ARPA
Essentially, we specify a revision to ARPANET Request for
This specification was developed over the course of one
A. Notational Conventions
B. Lexical Analysis of Messages
C. General Syntax of Messages
D. Syntax of General Addressee Items
E. Supporting Constructs
A. Address Fields
B. Reference Specification Fields
C. Other Fields and Syntactic Items
D. Dates and Times
B. Address Lists
C. Originator Items
D. Complete Headers
This standard specifies a syntax for text messages which are
This specification is intended strictly as a definition of
A distinction should be made between what the specification
Since there are many message systems which exist outside the
Messages are expected to consist of lines of text. No
No significant consideration has been given to questions of
A general "memo" framework is used. That is, a message
Such a framework severely constrains document tone and
This syntax is given in five parts. The first part
"<n>(element)" is equivalent to "<n>*<n>(element)"; that is,
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
To: "Joe Dokes & J. Harvey"
<ddd at Host>, JJV at BBN
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.
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
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.
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.
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.
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
- 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
Muhammed Ali at WBA
; ( 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
; CRLF => folding
/ "," / ";" / ":" / "\" / <"> ; word must be a ; quoted-string.
including CRLF> ; quoted-strings are ; NOT interpreted.
; chars or any ; quoted char.
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).
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.
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.
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).
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.
There are three types of brackets which must be well nested:
address specifications to indicate that the included list of addresses are to be treated as a group.
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",
"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.
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.
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.
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.
; first null line ; is message body
originator-fields ; & author id are *optional-field ; required: others ; are all optional
( "From" ":" mailbox ; Single author ["Reply-To" ":" #address] ) / ( "From" ":" 1#address ; Multiple authors & "Sender" ":" mailbox ; may have non-mach- ["Reply-To" ":" #address] ); ine addresses
"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
/ ( [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)
; be modified!
; at top of network ; hierarchy; left- ; most must be host
; network name or ; decimal address
/ "Wednesday" / "Wed" / "Thursday" / "Thu" / "Friday" / "Fri" / "Saturday" / "Sat" / "Sunday" / "Sun"
["-"] (2DIGIT /4DIGIT) ; e.g. 20 Aug 77
/ "March" / "Mar" / "April" / "Apr" / "May" / "June" / "Jun" / "July" / "Jul" / "August" / "Aug" / "September" / "Sep" / "October" / "Oct" / "November" / "Nov" / "December" / "Dec"
; (seconds optional)
; 0000 - 2359
; 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)
; Separation seman- ; tically = SPACE
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.
<address>. Constituent addresses must resolve to a host-
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:
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:
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.
<address>. The ":Include:" alternative also is valid.
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.
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:
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.
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.
WARNING: The standard allows only a subset of the combinations possible with the From, Sender,
and Reply-To fields. The limitation is intentional.
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.
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
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.
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.
(Extensive examples are provided in Section V.) This
This field contains the identity of the primary recipients of the message.
This field contains the identity of the secondary recipients of the message.
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.
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
From: Jones at Host
From: George Jones <Jones at Host> Sender: Secy at SHost
From: George Jones <Group at Host>
From: George Jones<Group at Host> Sender: Secy at Host
From: George Jones <Group at Host> Sender: Secy at Host Reply-To: Secy at Host
From: Sarah Friendly Sender: Secy at Host Reply-To: Jones at Host
From: George Jones Sender: Jones at Host Reply-To: Big-committee: Jones at Host, Smith at Other-Host, Doe at Somewhere-Else;
From: George Jones Sender: Secy at SHost
From: Big-committee: Jones at Host, Smith at Other-Host, Doe at Somewhere-Else; Sender: Secy at SHost
Date: 26 August 1976 1429-EDT
From: Jones at Host
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>
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>
/ (*phrase "<" #address ">" ) / (*phrase ":" #address ";" ) / (":" ("Include" / "Postal" / atom) ":" address) ALPHA = <any TELNET ASCII alphabetic character> atom = 1*<any CHAR except specials and CTLs>
/ "Wednesday" / "Wed" / "Thursday" / "Thu" / "Friday" / "Fri" / "Saturday" / "Sat" / "Sunday" / "Sun" delimiters = specials / comment / linear-white-space DIGIT = <any TELNET ASCII digit>
/ "March" / "Mar" / "April" / "Apr" / "May" / "June" / "Jun" / "July" / "Jul" / "August" / "Aug" / "September" / "Sep" / "October" / "Oct" / "November" / "Nov" / "December" / "Dec"
"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
( "From" ":" mailbox ["Reply-To" ":" #address] ) / ( "From" ":" 1#address "Sender" ":" mailbox ["Reply-To" ":" #address] )
/ "\" / <">
/ ( ["-"] (1ALPHA / "GMT" / "NST" / "AST" / "ADT" / "EST" / "EDT" / "CST" / "CDT" / "MST" / "MDT" / "PST" / "PDT" / "YST" / "YDT" / "HST" / "HDT" / "BST" / "BDT" )) <"> = <TELNET ASCII quote mark>
Some mail-reading software systems may wish to perform only
- 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
Headers occur before the message body and are terminated by
A line which continues a header field begins with a SPACE or
A field-name consists of one or more printable characters (excluding colon), each separated by one or more SPACES or HTABS.
11357; Augmentation Research Center, Stanford Research Institute: Menlo Park, August 1972.
ARPANET Request for Comments, No. 724, Network Information Center No. 37435; Augmentation Research Center, Stanford Research Institute: Menlo Park, May 1977.