rfc822 (4 of 5)
ron at brl-adm.UUCP
ron at brl-adm.UUCP
Tue May 20 14:00:13 AEST 1986
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 at 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 at 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
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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 at registry-A.registry-1.organization-X
and one recipient's address is:
recipient at registry-B.registry-1.organization-X
and another's is:
recipient at 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
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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
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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 at 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 at 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 at 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
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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 at 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
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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).
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APPENDIX
A. EXAMPLES
A.1. ADDRESSES
A.1.1. Alfred Neuman <Neuman at BBN-TENEXA>
A.1.2. Neuman at 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 at BBN-TENEXA" completely specifies the reci-
pient. The second example contains no superfluous informa-
tion, and, again, "Neuman at 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 at 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 at Group.Arpanet"
completely specifies the destination mailbox.
A.1.4. Wilt . (the Stilt) Chamberlain at 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 at Cordon-Bleu>,
Childs at WGBH.Boston, Galloping Gourmet@
ANT.Down-Under (Australian National Television),
Cheapie at Discount-Liquors;,
Cruisers: Port at Portugal, Jones at SEA;,
Another at Somewhere.SomeOrg
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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 at Group.Org
or
From: George Jones <Jones at 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 at Group>
Sender: Secy at 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 at Group.Org>
Sender: Secy at 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 at Host.Net>
Sender: Jones at Host
Reply-To: The Committee: Jones at Host.Net,
Smith at Other.Org,
Doe at Somewhere-Else;
Note that if George had not included himself in the
August 13, 1982 - 37 - RFC #822
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