brian@sdcsvax.UCSD.EDU (Brian Kantor) (09/01/87)
-
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
August 13, 1982 - 23 - RFC #822
Standard for ARPA Internet Text Messages
each receive new message identifiers.
4.6.2. IN-REPLY-TO
The contents of this field identify previous correspon-
dence which this message answers. Note that if message iden-
tifiers are used in this field, they must use the msg-id
specification format.
4.6.3. REFERENCES
The contents of this field identify other correspondence
which this message references. Note that if message identif-
iers are used, they must use the msg-id specification format.
4.6.4. KEYWORDS
This field contains keywords or phrases, separated by
commas.
4.7. OTHER FIELDS
4.7.1. SUBJECT
This is intended to provide a summary, or indicate the
nature, of the message.
4.7.2. COMMENTS
Permits adding text comments onto the message without
disturbing the contents of the message's body.
4.7.3. ENCRYPTED
Sometimes, data encryption is used to increase the
privacy of message contents. If the body of a message has
been encrypted, to keep its contents private, the "Encrypted"
field can be used to note the fact and to indicate the nature
of the encryption. The first <word> parameter indicates the
software used to encrypt the body, and the second, optional
<word> is intended to aid the recipient in selecting the
proper decryption key. This code word may be viewed as an
index to a table of keys held by the recipient.
Note: Unfortunately, headers must contain envelope, as well
as contents, information. Consequently, it is neces-
sary that they remain unencrypted, so that mail tran-
sport services may access them. Since names,
addresses, and "Subject" field contents may contain
August 13, 1982 - 24 - RFC #822
Standard for ARPA Internet Text Messages
sensitive information, this requirement limits total
message privacy.
Names of encryption software are registered with the Net-
work Information Center, SRI International, Menlo Park, Cali-
fornia.
4.7.4. EXTENSION-FIELD
A limited number of common fields have been defined in
this document. As network mail requirements dictate, addi-
tional fields may be standardized. To provide user-defined
fields with a measure of safety, in name selection, such
extension-fields will never have names that begin with the
string "X-".
Names of Extension-fields are registered with the Network
Information Center, SRI International, Menlo Park, California.
4.7.5. 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
Note: The prefatory string "X-" will never be used in the
names of Extension-fields. This provides user-defined
fields with a protected set of names.
August 13, 1982 - 25 - RFC #822
Standard for ARPA Internet Text Messages
5. DATE AND TIME SPECIFICATION
5.1. SYNTAX
date-time = [ day "," ] date time ; dd mm yy
; hh:mm:ss zzz
day = "Mon" / "Tue" / "Wed" / "Thu"
/ "Fri" / "Sat" / "Sun"
date = 1*2DIGIT month 2DIGIT ; day month year
; e.g. 20 Jun 82
month = "Jan" / "Feb" / "Mar" / "Apr"
/ "May" / "Jun" / "Jul" / "Aug"
/ "Sep" / "Oct" / "Nov" / "Dec"
time = hour zone ; ANSI and Military
hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT]
; 00:00:00 - 23:59:59
zone = "UT" / "GMT" ; Universal Time
; North American : UT
/ "EST" / "EDT" ; Eastern: - 5/ - 4
/ "CST" / "CDT" ; Central: - 6/ - 5
/ "MST" / "MDT" ; Mountain: - 7/ - 6
/ "PST" / "PDT" ; Pacific: - 8/ - 7
/ 1ALPHA ; Military: Z = UT;
; A:-1; (J not used)
; M:-12; N:+1; Y:+12
/ ( ("+" / "-") 4DIGIT ) ; Local differential
; hours+min. (HHMM)
5.2. SEMANTICS
If included, day-of-week must be the day implied by the date
specification.
Time zone may be indicated in several ways. "UT" is Univer-
sal Time (formerly called "Greenwich Mean Time"); "GMT" is per-
mitted as a reference to Universal Time. The military standard
uses a single character for each zone. "Z" is Universal Time.
"A" indicates one hour earlier, and "M" indicates 12 hours ear-
lier; "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 UT; the other uses common 3-character
strings for indicating time zones in North America.
August 13, 1982 - 26 - RFC #822
Standard for ARPA Internet Text Messages
6. ADDRESS SPECIFICATION
6.1. SYNTAX
address = mailbox ; one addressee
/ group ; named list
group = phrase ":" [#mailbox] ";"
mailbox = addr-spec ; simple address
/ phrase route-addr ; name & addr-spec
route-addr = "<" [route] addr-spec ">"
route = 1#("@" domain) ":" ; path-relative
addr-spec = local-part "@" domain ; global address
local-part = word *("." word) ; uninterpreted
; case-preserved
domain = sub-domain *("." sub-domain)
sub-domain = domain-ref / domain-literal
domain-ref = atom ; symbolic reference
6.2. SEMANTICS
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 their line printer and deliver
the output to the addressee's desk.
A mailbox specification comprises a person, system or pro-
cess name reference, a domain-dependent string, and a name-domain
reference. The name reference is optional and is usually used to
indicate the human name of a recipient. The name-domain refer-
ence specifies a sequence of sub-domains. The domain-dependent
string is uninterpreted, except by the final sub-domain; the rest
of the mail service merely transmits it as a literal string.
6.2.1. DOMAINS
A name-domain is a set of registered (mail) names. A name-
domain specification resolves to a subordinate name-domain
specification or to a terminal domain-dependent string.
Hence, domain specification is extensible, permitting any
number of registration levels.
August 13, 1982 - 27 - RFC #822
Standard for ARPA Internet Text Messages
Name-domains model a global, logical, hierarchical addressing
scheme. The model is logical, in that an address specifica-
tion is related to name registration and is not necessarily
tied to transmission path. The model's hierarchy is a
directed graph, called an in-tree, such that there is a single
path from the root of the tree to any node in the hierarchy.
If more than one path actually exists, they are considered to
be different addresses.
The root node is common to all addresses; consequently, it is
not referenced. Its children constitute "top-level" name-
domains. Usually, a service has access to its own full domain
specification and to the names of all top-level name-domains.
The "top" of the domain addressing hierarchy -- a child of the
root -- is indicated by the right-most field, in a domain
specification. Its child is specified to the left, its child
to the left, and so on.
Some groups provide formal registration services; these con-
stitute name-domains that are independent logically of
specific machines. In addition, networks and machines impli-
citly compose name-domains, since their membership usually is
registered in name tables.
In the case of formal registration, an organization implements
a (distributed) data base which provides an address-to-route
mapping service for addresses of the form:
person@registry.organization
Note that "organization" is a logical entity, separate from
any particular communication network.
A mechanism for accessing "organization" is universally avail-
able. That mechanism, in turn, seeks an instantiation of the
registry; its location is not indicated in the address specif-
ication. It is assumed that the system which operates under
the name "organization" knows how to find a subordinate regis-
try. The registry will then use the "person" string to deter-
mine where to send the mail specification.
The latter, network-oriented case permits simple, direct,
attachment-related address specification, such as:
user@host.network
Once the network is accessed, it is expected that a message
will go directly to the host and that the host will resolve
August 13, 1982 - 28 - RFC #822
Standard for ARPA Internet Text Messages
the user name, placing the message in the user's mailbox.
6.2.2. ABBREVIATED DOMAIN SPECIFICATION
Since any number of levels is possible within the domain
hierarchy, specification of a fully qualified address can
become inconvenient. This standard permits abbreviated domain
specification, in a special case:
For the address of the sender, call the left-most
sub-domain Level N. In a header address, if all of
the sub-domains above (i.e., to the right of) Level N
are the same as those of the sender, then they do not
have to appear in the specification. Otherwise, the
address must be fully qualified.
This feature is subject to approval by local sub-
domains. Individual sub-domains may require their
member systems, which originate mail, to provide full
domain specification only. When permitted, abbrevia-
tions may be present only while the message stays
within the sub-domain of the sender.
Use of this mechanism requires the sender's sub-domain
to reserve the names of all top-level domains, so that
full specifications can be distinguished from abbrevi-
ated specifications.
For example, if a sender's address is:
sender@registry-A.registry-1.organization-X
and one recipient's address is:
recipient@registry-B.registry-1.organization-X
and another's is:
recipient@registry-C.registry-2.organization-X
then ".registry-1.organization-X" need not be specified in the
the message, but "registry-C.registry-2" DOES have to be
specified. That is, the first two addresses may be abbrevi-
ated, but the third address must be fully specified.
When a message crosses a domain boundary, all addresses must
be specified in the full format, ending with the top-level
name-domain in the right-most field. It is the responsibility
of mail forwarding services to ensure that addresses conform
August 13, 1982 - 29 - RFC #822
Standard for ARPA Internet Text Messages
with this requirement. In the case of abbreviated addresses,
the relaying service must make the necessary expansions. It
should be noted that it often is difficult for such a service
to locate all occurrences of address abbreviations. For exam-
ple, it will not be possible to find such abbreviations within
the body of the message. The "Return-Path" field can aid
recipients in recovering from these errors.
Note: When passing any portion of an addr-spec onto a process
which does not interpret data according to this stan-
dard (e.g., mail protocol servers). There must be NO
LWSP-chars preceding or following the at-sign or any
delimiting period ("."), such as shown in the above
examples, and only ONE SPACE between contiguous
<word>s.
6.2.3. DOMAIN TERMS
A domain-ref must be THE official name of a registry, network,
or host. It is a symbolic reference, within a name sub-
domain. At times, it is necessary to bypass standard mechan-
isms for resolving such references, using more primitive
information, such as a network host address rather than its
associated host name.
To permit such references, this standard provides the domain-
literal construct. Its contents must conform with the needs
of the sub-domain in which it is interpreted.
Domain-literals which refer to domains within the ARPA Inter-
net specify 32-bit Internet addresses, in four 8-bit fields
noted in decimal, as described in Request for Comments #820,
"Assigned Numbers." For example:
[10.0.3.19]
Note: THE USE OF DOMAIN-LITERALS IS STRONGLY DISCOURAGED. It
is permitted only as a means of bypassing temporary
system limitations, such as name tables which are not
complete.
The names of "top-level" domains, and the names of domains
under in the ARPA Internet, are registered with the Network
Information Center, SRI International, Menlo Park, California.
6.2.4. DOMAIN-DEPENDENT LOCAL STRING
The local-part of an addr-spec in a mailbox specification
(i.e., the host's name for the mailbox) is understood to be
August 13, 1982 - 30 - RFC #822
Standard for ARPA Internet Text Messages
whatever the receiving mail protocol server allows. For exam-
ple, some systems do not understand mailbox references of the
form "P. D. Q. Bach", but others do.
This specification treats periods (".") as lexical separators.
Hence, their presence in local-parts which are not quoted-
strings, is detected. However, such occurrences carry NO
semantics. That is, if a local-part has periods within it, an
address parser will divide the local-part into several tokens,
but the sequence of tokens will be treated as one uninter-
preted unit. The sequence will be re-assembled, when the
address is passed outside of the system such as to a mail pro-
tocol service.
For example, the address:
First.Last@Registry.Org
is legal and does not require the local-part to be surrounded
with quotation-marks. (However, "First Last" DOES require
quoting.) The local-part of the address, when passed outside
of the mail system, within the Registry.Org domain, is
"First.Last", again without quotation marks.
6.2.5. BALANCING LOCAL-PART AND DOMAIN
In some cases, the boundary between local-part and domain can
be flexible. The local-part may be a simple string, which is
used for the final determination of the recipient's mailbox.
All other levels of reference are, therefore, part of the
domain.
For some systems, in the case of abbreviated reference to the
local and subordinate sub-domains, it may be possible to
specify only one reference within the domain part and place
the other, subordinate name-domain references within the
local-part. This would appear as:
mailbox.sub1.sub2@this-domain
Such a specification would be acceptable to address parsers
which conform to RFC #733, but do not support this newer
Internet standard. While contrary to the intent of this stan-
dard, the form is legal.
Also, some sub-domains have a specification syntax which does
not conform to this standard. For example:
sub-net.mailbox@sub-domain.domain
August 13, 1982 - 31 - RFC #822
Standard for ARPA Internet Text Messages
uses a different parsing sequence for local-part than for
domain.
Note: As a rule, the domain specification should contain
fields which are encoded according to the syntax of
this standard and which contain generally-standardized
information. The local-part specification should con-
tain only that portion of the address which deviates
from the form or intention of the domain field.
6.2.6. MULTIPLE MAILBOXES
An individual may have several mailboxes and wish to receive
mail at whatever mailbox is convenient for the sender to
access. This standard does not provide a means of specifying
"any member of" a list of mailboxes.
A set of individuals may wish to receive mail as a single unit
(i.e., a distribution list). The <group> construct permits
specification of such a list. Recipient mailboxes are speci-
fied within the bracketed part (":" - ";"). A copy of the
transmitted message is to be sent to each mailbox listed.
This standard does not permit recursive specification of
groups within groups.
While a list must be named, it is not required that the con-
tents of the list be included. In this case, the <address>
serves only as an indication of group distribution and would
appear in the form:
name:;
Some mail services may provide a group-list distribution
facility, accepting a single mailbox reference, expanding it
to the full distribution list, and relaying the mail to the
list's members. This standard provides no additional syntax
for indicating such a service. Using the <group> address
alternative, while listing one mailbox in it, can mean either
that the mailbox reference will be expanded to a list or that
there is a group with one member.
6.2.7. EXPLICIT PATH SPECIFICATION
At times, a message originator may wish to indicate the
transmission path that a message should follow. This is
called source routing. The normal addressing scheme, used in
an addr-spec, is carefully separated from such information;
the <route> portion of a route-addr is provided for such occa-
sions. It specifies the sequence of hosts and/or transmission
August 13, 1982 - 32 - RFC #822
Standard for ARPA Internet Text Messages
services that are to be traversed. Both domain-refs and
domain-literals may be used.
Note: The use of source routing is discouraged. Unless the
sender has special need of path restriction, the choice
of transmission route should be left to the mail tran-
sport service.
6.3. RESERVED ADDRESS
It often is necessary to send mail to a site, without know-
ing any of its valid addresses. For example, there may be mail
system dysfunctions, or a user may wish to find out a person's
correct address, at that site.
This standard specifies a single, reserved mailbox address
(local-part) which is to be valid at each site. Mail sent to
that address is to be routed to a person responsible for the
site's mail system or to a person with responsibility for general
site operation. The name of the reserved local-part address is:
Postmaster
so that "Postmaster@domain" is required to be valid.
Note: This reserved local-part must be matched without sensi-
tivity to alphabetic case, so that "POSTMASTER", "postmas-
ter", and even "poStmASteR" is to be accepted.
August 13, 1982 - 33 - RFC #822
Standard for ARPA Internet Text Messages
7. BIBLIOGRAPHY
ANSI. "USA Standard Code for Information Interchange," X3.4.
American National Standards Institute: New York (1968). Also
in: Feinler, E. and J. Postel, eds., "ARPANET Protocol Hand-
book", NIC 7104.
ANSI. "Representations of Universal Time, Local Time Differen-
tials, and United States Time Zone References for Information
Interchange," X3.51-1975. American National Standards Insti-
tute: New York (1975).
Bemer, R.W., "Time and the Computer." In: Interface Age (Feb.
1979).
Bennett, C.J. "JNT Mail Protocol". Joint Network Team, Ruther-
ford and Appleton Laboratory: Didcot, England.
Bhushan, A.K., Pogran, K.T., Tomlinson, R.S., and White, J.E.
"Standardizing Network Mail Headers," ARPANET Request for
Comments No. 561, Network Information Center No. 18516; SRI
International: Menlo Park (September 1973).
Birrell, A.D., Levin, R., Needham, R.M., and Schroeder, M.D.
"Grapevine: An Exercise in Distributed Computing," Communica-
tions of the ACM 25, 4 (April 1982), 260-274.
Crocker, D.H., Vittal, J.J., Pogran, K.T., Henderson, D.A.
"Standard for the Format of ARPA Network Text Message,"
ARPANET Request for Comments No. 733, Network Information
Center No. 41952. SRI International: Menlo Park (November
1977).
Feinler, E.J. and Postel, J.B. ARPANET Protocol Handbook, Net-
work Information Center No. 7104 (NTIS AD A003890). SRI
International: Menlo Park (April 1976).
Harary, F. "Graph Theory". Addison-Wesley: Reading, Mass.
(1969).
Levin, R. and Schroeder, M. "Transport of Electronic Messages
through a Network," TeleInformatics 79, pp. 29-33. North
Holland (1979). Also as Xerox Palo Alto Research Center
Technical Report CSL-79-4.
Myer, T.H. and Henderson, D.A. "Message Transmission Protocol,"
ARPANET Request for Comments, No. 680, Network Information
Center No. 32116. SRI International: Menlo Park (1975).
August 13, 1982 - 34 - RFC #822
Standard for ARPA Internet Text Messages
NBS. "Specification of Message Format for Computer Based Message
Systems, Recommended Federal Information Processing Standard."
National Bureau of Standards: Gaithersburg, Maryland
(October 1981).
NIC. Internet Protocol Transition Workbook. Network Information
Center, SRI-International, Menlo Park, California (March
1982).
Oppen, D.C. and Dalal, Y.K. "The Clearinghouse: A Decentralized
Agent for Locating Named Objects in a Distributed Environ-
ment," OPD-T8103. Xerox Office Products Division: Palo Alto,
CA. (October 1981).
Postel, J.B. "Assigned Numbers," ARPANET Request for Comments,
No. 820. SRI International: Menlo Park (August 1982).
Postel, J.B. "Simple Mail Transfer Protocol," ARPANET Request
for Comments, No. 821. SRI International: Menlo Park (August
1982).
Shoch, J.F. "Internetwork naming, addressing and routing," in
Proc. 17th IEEE Computer Society International Conference, pp.
72-79, Sept. 1978, IEEE Cat. No. 78 CH 1388-8C.
Su, Z. and Postel, J. "The Domain Naming Convention for Internet
User Applications," ARPANET Request for Comments, No. 819.
SRI International: Menlo Park (August 1982).
August 13, 1982 - 35 - RFC #822
Standard for ARPA Internet Text Messages
APPENDIX
A. EXAMPLES
A.1. ADDRESSES
A.1.1. Alfred Neuman <Neuman@BBN-TENEXA>
A.1.2. Neuman@BBN-TENEXA
These two "Alfred Neuman" examples have identical seman-
tics, as far as the operation of the local host's mail sending
(distribution) program (also sometimes called its "mailer")
and the remote host's mail protocol server are concerned. In
the first example, the "Alfred Neuman" is ignored by the
mailer, as "Neuman@BBN-TENEXA" completely specifies the reci-
pient. The second example contains no superfluous informa-
tion, and, again, "Neuman@BBN-TENEXA" is the intended reci-
pient.
Note: When the message crosses name-domain boundaries, then
these specifications must be changed, so as to indicate
the remainder of the hierarchy, starting with the top
level.
A.1.3. "George, Ted" <Shared@Group.Arpanet>
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, because "Shared@Group.Arpanet"
completely specifies the destination mailbox.
A.1.4. Wilt . (the Stilt) Chamberlain@NBA.US
The "(the Stilt)" is a comment, which is NOT included in
the destination mailbox address handed to the originating
system's mailer. The local-part of the address is the string
"Wilt.Chamberlain", with NO space between the first and second
words.
A.1.5. Address Lists
Gourmets: Pompous Person <WhoZiWhatZit@Cordon-Bleu>,
Childs@WGBH.Boston, Galloping Gourmet@
ANT.Down-Under (Australian National Television),
Cheapie@Discount-Liquors;,
Cruisers: Port@Portugal, Jones@SEA;,
Another@Somewhere.SomeOrg
August 13, 1982 - 36 - RFC #822
Standard for ARPA Internet Text Messages
This group list example points out the use of comments and the
mixing of addresses and groups.
A.2. ORIGINATOR ITEMS
A.2.1. Author-sent
George Jones logs into his host as "Jones". He sends
mail himself.
From: Jones@Group.Org
or
From: George Jones <Jones@Group.Org>
A.2.2. Secretary-sent
George Jones logs in as Jones on his host. His secre-
tary, who logs in as Secy sends mail for him. Replies to the
mail should go to George.
From: George Jones <Jones@Group>
Sender: Secy@Other-Group
A.2.3. Secretary-sent, for user of shared directory
George Jones' secretary sends mail for George. Replies
should go to George.
From: George Jones<Shared@Group.Org>
Sender: Secy@Other-Group
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.
A.2.4. Committee activity, with one author
George is a member of a committee. He wishes to have any
replies to his message go to all committee members.
From: George Jones <Jones@Host.Net>
Sender: Jones@Host
Reply-To: The Committee: Jones@Host.Net,
Smith@Other.Org,
Doe@Somewhere-Else;
Note that if George had not included himself in the
August 13, 1982 - 37 - RFC #822
Standard for ARPA Internet Text Messages
enumeration of The Committee, he would not have gotten an
implicit reply; the presence of the "Reply-to" field SUPER-
SEDES the sending of a reply to the person named in the "From"
field.
A.2.5. Secretary acting as full agent of author
George Jones asks his secretary (Secy@Host) to send a
message for him in his capacity as Group. He wants his secre-
tary to handle all replies.
From: George Jones <Group@Host>
Sender: Secy@Host
Reply-To: Secy@Host
A.2.6. Agent for user without online mailbox
A friend of George's, Sarah, is visiting. George's
secretary sends some mail to a friend of Sarah in computer-
land. Replies should go to George, whose mailbox is Jones at
Registry.
From: Sarah Friendly <Secy@Registry>
Sender: Secy-Name <Secy@Registry>
Reply-To: Jones@Registry.
A.2.7. Agent for member of a committee
George's secretary sends out a message which was authored
jointly by all the members of a committee. Note that the name
of the committee cannot be specified, since <group> names are
not permitted in the From field.
From: Jones@Host,
Smith@Other-Host,
Doe@Somewhere-Else
Sender: Secy@SHost
August 13, 1982 - 38 - RFC #822
Standard for ARPA Internet Text Messages
A.3. COMPLETE HEADERS
A.3.1. Minimum required
Date: 26 Aug 76 1429 EDT Date: 26 Aug 76 1429 EDT
From: Jones@Registry.Org or From: Jones@Registry.Org
Bcc: To: Smith@Registry.Org
Note that the "Bcc" field may be empty, while the "To" field
is required to have at least one address.
A.3.2. Using some of the additional fields
Date: 26 Aug 76 1430 EDT
From: George Jones<Group@Host>
Sender: Secy@SHOST
To: "Al Neuman"@Mad-Host,
Sam.Irving@Other-Host
Message-ID: <some.string@SHOST>
A.3.3. About as complex as you're going to get
Date : 27 Aug 76 0932 PDT
From : Ken Davis <KDavis@This-Host.This-net>
Subject : Re: The Syntax in the RFC
Sender : KSecy@Other-Host
Reply-To : Sam.Irving@Reg.Organization
To : George Jones <Group@Some-Reg.An-Org>,
Al.Neuman@MAD.Publisher
cc : Important folk:
Tom Softwood <Balsa@Tree.Root>,
"Sam Irving"@Other-Host;,
Standard Distribution:
/main/davis/people/standard@Other-Host,
"<Jones>standard.dist.3"@Tops-20-Host>;
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@DBM.Group>, George's message
X-Special-action: This is a sample of user-defined field-
names. There could also be a field-name
"Special-action", but its name might later be
preempted
Message-ID: <4231.629.XYzi-What@Other-Host>
August 13, 1982 - 39 - RFC #822
Standard for ARPA Internet Text Messages
B. SIMPLE FIELD 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:
o Header fields from the message body,
o Beginnings of fields from lines which continue fields,
o Field-names from field-contents.
The abbreviated set of syntactic rules which follows will
suffice for this purpose. It describes a limited view of mes-
sages and is a subset of the syntactic rules provided in the main
part of this specification. One small exception is that the con-
tents of field-bodies consist only of text:
B.1. SYNTAX
message = *field *(CRLF *text)
field = field-name ":" [field-body] CRLF
field-name = 1*<any CHAR, excluding CTLs, SPACE, and ":">
field-body = *text [CRLF LWSP-char field-body]
B.2. 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, space, and control-characters). A field-name
MUST be contained on one line. Upper and lower case are not dis-
tinguished when comparing field-names.
August 13, 1982 - 40 - RFC #822
Standard for ARPA Internet Text Messages
C. DIFFERENCES FROM RFC #733
The following summarizes the differences between this stan-
dard and the one specified in Arpanet Request for Comments #733,
"Standard for the Format of ARPA Network Text Messages". The
differences are listed in the order of their occurrence in the
current specification.
C.1. FIELD DEFINITIONS
C.1.1. FIELD NAMES
These now must be a sequence of printable characters. They
may not contain any LWSP-chars.
C.2. LEXICAL TOKENS
C.2.1. SPECIALS
The characters period ("."), left-square bracket ("["), and
right-square bracket ("]") have been added. For presentation
purposes, and when passing a specification to a system that
does not conform to this standard, periods are to be contigu-
ous with their surrounding lexical tokens. No linear-white-
space is permitted between them. The presence of one LWSP-
char between other tokens is still directed.
C.2.2. ATOM
Atoms may not contain SPACE.
C.2.3. SPECIAL TEXT
ctext and qtext have had backslash ("\") added to the list of
prohibited characters.
C.2.4. DOMAINS
The lexical tokens <domain-literal> and <dtext> have been
added.
C.3. MESSAGE SPECIFICATION
C.3.1. TRACE
The "Return-path:" and "Received:" fields have been specified.
August 13, 1982 - 41 - RFC #822
Standard for ARPA Internet Text Messages
C.3.2. FROM
The "From" field must contain machine-usable addresses (addr-
spec). Multiple addresses may be specified, but named-lists
(groups) may not.
C.3.3. RESENT
The meta-construct of prefacing field names with the string
"Resent-" has been added, to indicate that a message has been
forwarded by an intermediate recipient.
C.3.4. DESTINATION
A message must contain at least one destination address field.
"To" and "CC" are required to contain at least one address.
C.3.5. IN-REPLY-TO
The field-body is no longer a comma-separated list, although a
sequence is still permitted.
C.3.6. REFERENCE
The field-body is no longer a comma-separated list, although a
sequence is still permitted.
C.3.7. ENCRYPTED
A field has been specified that permits senders to indicate
that the body of a message has been encrypted.
C.3.8. EXTENSION-FIELD
Extension fields are prohibited from beginning with the char-
acters "X-".
C.4. DATE AND TIME SPECIFICATION
C.4.1. SIMPLIFICATION
Fewer optional forms are permitted and the list of three-
letter time zones has been shortened.
C.5. ADDRESS SPECIFICATION
August 13, 1982 - 42 - RFC #822
Standard for ARPA Internet Text Messages
C.5.1. ADDRESS
The use of quoted-string, and the ":"-atom-":" construct, have
been removed. An address now is either a single mailbox
reference or is a named list of addresses. The latter indi-
cates a group distribution.
C.5.2. GROUPS
Group lists are now required to to have a name. Group lists
may not be nested.
C.5.3. MAILBOX
A mailbox specification may indicate a person's name, as
before. Such a named list no longer may specify multiple
mailboxes and may not be nested.
C.5.4. ROUTE ADDRESSING
Addresses now are taken to be absolute, global specifications,
independent of transmission paths. The <route> construct has
been provided, to permit explicit specification of transmis-
sion path. RFC #733's use of multiple at-signs ("@") was
intended as a general syntax for indicating routing and/or
hierarchical addressing. The current standard separates these
specifications and only one at-sign is permitted.
C.5.5. AT-SIGN
The string " at " no longer is used as an address delimiter.
Only at-sign ("@") serves the function.
C.5.6. DOMAINS
Hierarchical, logical name-domains have been added.
C.6. RESERVED ADDRESS
The local-part "Postmaster" has been reserved, so that users can
be guaranteed at least one valid address at a site.
August 13, 1982 - 43 - RFC #822
Standard for ARPA Internet Text Messages
D. ALPHABETICAL LISTING OF SYNTAX RULES
address = mailbox ; one addressee
/ group ; named list
addr-spec = local-part "@" domain ; global address
ALPHA = <any ASCII alphabetic character>
; (101-132, 65.- 90.)
; (141-172, 97.-122.)
atom = 1*<any CHAR except specials, SPACE and CTLs>
authentic = "From" ":" mailbox ; Single author
/ ( "Sender" ":" mailbox ; Actual submittor
"From" ":" 1#mailbox) ; Multiple authors
; or not sender
CHAR = <any ASCII character> ; ( 0-177, 0.-127.)
comment = "(" *(ctext / quoted-pair / comment) ")"
CR = <ASCII CR, carriage return> ; ( 15, 13.)
CRLF = CR LF
ctext = <any CHAR excluding "(", ; => may be folded
")", "\" & CR, & including
linear-white-space>
CTL = <any ASCII control ; ( 0- 37, 0.- 31.)
character and DEL> ; ( 177, 127.)
date = 1*2DIGIT month 2DIGIT ; day month year
; e.g. 20 Jun 82
dates = orig-date ; Original
[ resent-date ] ; Forwarded
date-time = [ day "," ] date time ; dd mm yy
; hh:mm:ss zzz
day = "Mon" / "Tue" / "Wed" / "Thu"
/ "Fri" / "Sat" / "Sun"
delimiters = specials / linear-white-space / comment
destination = "To" ":" 1#address ; Primary
/ "Resent-To" ":" 1#address
/ "cc" ":" 1#address ; Secondary
/ "Resent-cc" ":" 1#address
/ "bcc" ":" #address ; Blind carbon
/ "Resent-bcc" ":" #address
DIGIT = <any ASCII decimal digit> ; ( 60- 71, 48.- 57.)
domain = sub-domain *("." sub-domain)
domain-literal = "[" *(dtext / quoted-pair) "]"
domain-ref = atom ; symbolic reference
dtext = <any CHAR excluding "[", ; => may be folded
"]", "\" & CR, & including
linear-white-space>
extension-field =
<Any field which is defined in a document
published as a formal extension to this
specification; none will have names beginning
with the string "X-">
August 13, 1982 - 44 - RFC #822
Standard for ARPA Internet Text Messages
field = field-name ":" [ field-body ] CRLF
fields = dates ; Creation time,
source ; author id & one
1*destination ; address required
*optional-field ; others optional
field-body = field-body-contents
[CRLF LWSP-char field-body]
field-body-contents =
<the 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 = 1*<any CHAR, excluding CTLs, SPACE, and ":">
group = phrase ":" [#mailbox] ";"
hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT]
; 00:00:00 - 23:59:59
HTAB = <ASCII HT, horizontal-tab> ; ( 11, 9.)
LF = <ASCII LF, linefeed> ; ( 12, 10.)
linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE
; CRLF => folding
local-part = word *("." word) ; uninterpreted
; case-preserved
LWSP-char = SPACE / HTAB ; semantics = SPACE
mailbox = addr-spec ; simple address
/ phrase route-addr ; name & addr-spec
message = fields *( CRLF *text ) ; Everything after
; first null line
; is message body
month = "Jan" / "Feb" / "Mar" / "Apr"
/ "May" / "Jun" / "Jul" / "Aug"
/ "Sep" / "Oct" / "Nov" / "Dec"
msg-id = "<" addr-spec ">" ; Unique message id
optional-field =
/ "Message-ID" ":" msg-id
/ "Resent-Message-ID" ":" msg-id
/ "In-Reply-To" ":" *(phrase / msg-id)
/ "References" ":" *(phrase / msg-id)
/ "Keywords" ":" #phrase
/ "Subject" ":" *text
/ "Comments" ":" *text
/ "Encrypted" ":" 1#2word
/ extension-field ; To be defined
/ user-defined-field ; May be pre-empted
orig-date = "Date" ":" date-time
originator = authentic ; authenticated addr
[ "Reply-To" ":" 1#address] )
phrase = 1*word ; Sequence of words
August 13, 1982 - 45 - RFC #822
Standard for ARPA Internet Text Messages
qtext = <any CHAR excepting <">, ; => may be folded
"\" & CR, and including
linear-white-space>
quoted-pair = "\" CHAR ; may quote any char
quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or
; quoted chars.
received = "Received" ":" ; one per relay
["from" domain] ; sending host
["by" domain] ; receiving host
["via" atom] ; physical path
*("with" atom) ; link/mail protocol
["id" msg-id] ; receiver msg id
["for" addr-spec] ; initial form
";" date-time ; time received
resent = resent-authentic
[ "Resent-Reply-To" ":" 1#address] )
resent-authentic =
= "Resent-From" ":" mailbox
/ ( "Resent-Sender" ":" mailbox
"Resent-From" ":" 1#mailbox )
resent-date = "Resent-Date" ":" date-time
return = "Return-path" ":" route-addr ; return address
route = 1#("@" domain) ":" ; path-relative
route-addr = "<" [route] addr-spec ">"
source = [ trace ] ; net traversals
originator ; original mail
[ resent ] ; forwarded
SPACE = <ASCII SP, space> ; ( 40, 32.)
specials = "(" / ")" / "<" / ">" / "@" ; Must be in quoted-
/ "," / ";" / ":" / "\" / <"> ; string, to use
/ "." / "[" / "]" ; within a word.
sub-domain = domain-ref / domain-literal
text = <any CHAR, including bare ; => atoms, specials,
CR & bare LF, but NOT ; comments and
including CRLF> ; quoted-strings are
; NOT recognized.
time = hour zone ; ANSI and Military
trace = return ; path to sender
1*received ; receipt tags
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
pre-empted by published extensions>
word = atom / quoted-string
August 13, 1982 - 46 - RFC #822
Standard for ARPA Internet Text Messages
zone = "UT" / "GMT" ; Universal Time
; North American : UT
/ "EST" / "EDT" ; Eastern: - 5/ - 4
/ "CST" / "CDT" ; Central: - 6/ - 5
/ "MST" / "MDT" ; Mountain: - 7/ - 6
/ "PST" / "PDT" ; Pacific: - 8/ - 7
/ 1ALPHA ; Military: Z = UT;
<"> = <ASCII quote mark> ; ( 42, 34.)
August 13, 1982 - 47 - RFC #822
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