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RFC 754 J. Postel
ISI
6 April 1979
Out-of-Net Host Addresses for Mail
There is now interest in sustantially extending the scope of the
computer mail system used in the ARPANET to allow communication of
voice, fax, graphics, as well as text information between users in
different networks as wells as within the ARPANET.
The discussion of a transition from the current ARPANET sndmsg
environment and mechanisms to a more general internet environment and
richer mechanisms must consider techniques for continued activity during
the transition. In addition, there is a current need for a mechanism to
support the interaction of the several already existing NSW-like message
environments with the ARPANET message environment.
This memo discusses some possible alternatives for computer mail
addressing for hosts outside the ARPANET in the short term. This memo
is hopelessly Tenex oriented in its descriptions and examples.
It helps to keep a few goals in mind while considering the alternative
solutions:
Goals:
1) Minimum Change to Existing Software.
2) Maximum User Acceptance.
3) Maximum Compatibility with the future Internet Message
Environment.
4) Minimum Special Transition Software.
These goals are to some degree incompatible, so the evaluation should be
expected to involve a trade off.
At this point, it would be good to have a model of the current situation
and mechanisms of the ARPANET message environment. It is assumed the
reader understands it well enough to dispense with a long description of
how a message gets from A to B. The important thing is to note the
types of players in the picture. There are:
message composition (or sending) programs (e.g., Hermes, SNDMSG), in
general there are several message composition programs for each type
of operating system or host in the network,
Postel [page 1]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
mailers,
mail servers (i.e., FTP servers) that receive the mail coming into at
host and deposit it in mailboxes,
message processing (or reading) programs (e.g., Hermes, MSG, RD), in
general there are several message processing programs for each type
of operating system or host in the network, and note that the more
developed mail are both reading and sending programs.
Messages are transmitted as a character string to an address which is
specified "outside" the message. The destination host ("YYY") is
specified to the sending (or user) FTP as the argument of the "open
connection" command, and the destination user ("XXX") is specified to
the receiving (or server) FTP as the argument of the "MAIL" (or "MLFL")
command. In Tenex, when mail is queued this outside information is
saved in the file name ("[---].XXX@YYY").
The proposed solutions are briefly characterized.
Proposed Solutions:
This first pass at describing the solutions is rather brief and
intended to set the scene for a subsequent discussion based on
examples.
A) SINGLE MAILBOX
This solution suggests that all mail for another network be routed
to a single mailbox on a forwarding host on the ARPANET. The FTP
server would naturally put all the mail for this mailbox into a
single file to be examined by a routing deamon process. The
routing deamon process would use information in new header lines
to determine the actual destination.
Format:
Outside: [---].NSW-MAIL@FWDR
Inside: To: NSW-MAIL@FWDR
From: Sam@ISIB
NSW-User: Joe
Postel [page 2]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
B) GLOBAL NAMES INSIDE
This proposal suggests that all mail for users in another network
be sent to a single mailbox on a forwarding host. The FTP server
would naturally put all the mail for this mailbox into a single
file to be examined by a routing deamon process. The routing
deamon process would use information in existing header lines to
determine the actual destination.
Format:
Outside: [---].NSW-MAIL@FWDR
Inside: To: Joe@NSW
From: Sam@ISIB
C) GLOBAL NAMES OUTSIDE
This proposal suggests that mail for users in another network be
sent to distinct per user mailbox names on a forwarding host. The
FTP server would somehow put all the mail for these mailboxes into
a single file to be examined by a routing deamon process. The
routing deamon process would use information in existing header
lines to determine the actual destination.
Format:
Outside: [---].Joe@FWDR or [---].Joe@NSW
Inside: To: Joe@NSW
From: Sam@ISIB
D) STRUCTURED NAMES
This proposal suggests that mail for users in another network be
sent to distinct per user mailbox names on a forwarding host,
however, these mailbox names would have a common "network" part
and a unique "user" part. By recognizing the common part the FTP
server would put the mail and the mailbox name into a single file
to be examined by a routing deamon process. The routing deamon
process would use mailbox name information to determine the actual
destination.
Postel [page 3]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
Format:
Outside: [---].NSW-Joe@FWDR
Inside: To: NSW-Joe@FWDR
From: Sam@ISIB
Before further examination of the advantages and disadvantages of these
proposals, it would be well to have some more detailed criteria in mind
to help expose the degree to which the goals are met.
Criteria:
1) What changes are needed?
2) How many instances of the change need to be implemented?
3) What information does the routing deamon use?
4) How does the "answer" command work?
5) How is the name space used?
It is particularly instructive to work through examples with a
mixture of mailbox destinations in the ARPANET and other networks in
each of the "To:" and "CC:" fields and to see what happens when one
wants to send an answer to all, just the "To:", or just the "CC:", or
just the "From:" or "Sender:" mailboxes.
Solutions Reconsidered:
It is easier to talk about these things in terms of examples. In the
following "NSW" is an example of a network name. "FWDR" is a host
name, or nickname for the forwarding host. Also note that for all of
these solutions it is assumed that host tables can have alternate or
nicknames for hosts, e.g., FWDR could map to 86 while ISI also maps
to 86, although this is not essential.
In addition, all these solutions provide a single forwarding point
from the ARPANET into the destination net.
All forwarded messages are handled by a routing deamon which lives in
the FWDR host.
Also note that the information shown as the "outside" information is
the Tenex representation. The key thing is the mailbox argument
value that is passed to the FTP server is the one in the string
Postel [page 4]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
"[---].XXX@YYY", not anything from the header. Only the string "XXX"
is passed to the FTP server.
A) SINGLE MAILBOX
Example:
Outside: [---].NSW-MAIL@FWDR
Inside: To: NSW-MAIL@FWDR,Bill@ISIA
CC: Jeff@ISIB
From: Joe@ISIB
NSW-User-To: SAM,Fred
NSW-User-CC: Bob,Mike
or
Outside: [---].NSW-MAIL@FWDR
Inside: To: NSW-MAIL@FWDR,Bill@ISIA
CC: Jeff@ISIB
From: NSW-MAIL@FWDR
NSW-User-To: SAM,Fred
NSW-User-CC: Bob,Mike
NSW-User-From: Paul
Every mail composition program has to change to make it easy for
users to put the "NSW-User:" line in the header. Every mail
reading program has to change to notice and make use of this line.
In an "answer" command the mail processing program has to know to
copy this line into the answer message. The deamon has to examine
the inside message header to find the "NSW-User:" line and forward
the message to the users listed there. If there is a message that
has both NSW and ARPANET mailboxes in both the "To:" and "CC:"
lines, then it seems there must be both a "NSW-Users-To:" and a
"NSW-Users-CC:" lines if it is to be possible to send an answer to
just the users in the "To:" lines. If there is another network,
e.g. PRNET, then another set of header lines must be introduced,
e.g. PRNET-USER-To: etc., that is up to four new lines per network
(To, CC, From, Sender).
This solution has the advantage of saving some transmissions:
when several of the destination mailboxes are in NSW, the sending
program sends just one copy to the FWDR and routing deamon, the
routing deamon sends copies to all NSW users it finds. If this is
not done, the deamon would have difficulty avoiding sending
multiple copies to each destination user.
Postel [page 5]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
A problem arises about acknowledgements of mail receipt. First
the normal ARPANET message delivery mechanisms will say the mail
is delivered when the FTP server puts the mail in the file for the
routing deamon to examine. Second if the routing deamon discovers
an message is to be forwarded to a nonexistent user, care must be
used to notify the original sender unambiguously.
Changes:
all composition programs
B) GLOBAL NAMES INSIDE
Example:
Outside: [---].NSW-MAIL@FWDR
Inside: To: Joe@NSW, Bill@ISIA, Fred@NSW
CC: Mike@NSW, Paul@NSW, John@ISIB
From: Sam@ISIB
Every mail composition program has to know that NSW is a very
special host name, for which it uses a different mailbox argument
and sends to the FWDR host. The FTP server naturally puts all the
NSW mail into a single mailbox file which the routing deamon
examines. The "answer" command works fine. The routing deamon
has to look at the inside header to determine where to forward the
messages. It has to check the "To:" and "CC:" lines.
The sending programs must also send just one copy to the FWDR and
routing deamon, the routing deamon will send copies to all NSW
users it finds. If this is not done, the deamon would have
difficulty avoiding sending multiple copies to each destination
user. This is an advantage in terms of number of transmissions.
A problem arises about acknowledgements of mail receipt. First
the normal ARPANET message delivery mechanisms will say the mail
is delivered when the FTP server puts the mail in the file for the
routing deamon to examine. Second if the routing deamon discovers
an message is to be forwarded to a nonexistent user, care must be
used to notify the original sender unambiguously.
Changes:
all sending programs
Postel [page 6]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
C) GLOBAL NAMES OUTSIDE
Example:
Outside: [---].Joe@NSW
Inside: To: Joe@NSW, Bill@ISIA, Fred@NSW
CC: Mike@NSW, Paul@NSW, John@ISIB
From: Sam@ISIB
No changes to mail composition or processing programs are needed.
The FTP server has to put all the NSW users mail into a single
mailbox file which the routing deamon examines. The cheapest way
to do this is to put all the names of the NSW users in the ARPANET
user forwarding file with the same destination ARPANET mailbox.
This means the local users of the FWDR host and the users in the
destination networks share the name space for user names. The
routing deamon has to look at the inside header to determine where
to forward the messages. It has to check the "To:" and "CC:"
lines.
This appears to be the solution with the minimum change to
existing software. The "answer" command works fine.
There is a problem with the name space, for example, if ISIA
serves as FWDR host, then Fred@ISI and Fred@NSW cannot co-exist.
Further, there is the database update problem. Every time a new
user is added to NSW or any of the hosts in any of the nets that
the FWDR host serves the forwarding file at the FWDR host has to
be updated. The names added have to be unique so all user names
assigned in NSW and all the hosts on all the networks served by
the same FWDR host have to be oked by the "forwarding file data
base administrator" before they can actually be used. Also note
that Fred@NSW and Fred@PRNET cannot be routed through the same
FWDR host.
This doesn't work too well, if the sending programs are not
changed they will send one copy of this message for each NSW user
and all these copies will end up in the file to be examined by the
routing deamon. If the FTP server code is not changed the outside
information will be lost and the routing deamon will have no idea
which NSW user this copy is for. To do the job right with the
information available the routing deamon would have to keep a
substantial record about each message it handled checking to see
if it received for, and send a copy to, each intended destination
user.
Postel [page 7]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
A problem arises about acknowledgements of mail receipt. First
the normal ARPANET message delivery mechanisms will say the mail
is delivered when the FTP server puts the mail in the file for the
routing deamon to examine. Second if the routing deamon discovers
an message is to be forwarded to a nonexistent user, care must be
used to notify the original sender unambiguously.
Changes:
ARPANET user forwarding file at FWDR host
D) STRUCTURED NAMES
Example:
Outside: [---].NSW-Joe@NSW
Inside: To: NSW-Joe@NSW, Bill@ISIA, NSW-Fred@NSW
CC: NSW-Mike@NSW, NSW-Paul@NSW, John@ISIB
From: Sam@ISIB
No changes to mail composition or processing programs are needed.
The FTP server has to put all the NSW-x users mail into a single
file which the routing deamon examines. The FTP server can do
this on the recognition of the "NSW-" prefix without knowing all
the legal individual users. In addition the FTP server puts the
mailbox argument into the file with the message. This is
necessary to avoid the loss of the "outside" information. The
routing deamon can then look at the mailbox argument to determine
where to forward the messages. It need not look at the inside of
the message at all. The "answer" command works fine.
A problem arises about acknowledgements of mail receipt. First
the normal ARPANET message delivery mechanisms will say the mail
is delivered when the FTP server puts the mail in the file for the
routing deamon to examine. However, if the routing deamon
discovers an message is to be forwarded to a nonexistent user, the
deamon can easily tell the original sender the exact destination
user that is unreachable.
Changes:
FTP server at FWDR host
Postel [page 8]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
Summary:
A B C D
Single Global Global Structured
Mailbox Names Names Names
Inside Outside
Criteria:
1) What changes? Composer Composer None FTP server
2) How many? 100 100 0 1
3) Routing information? New Old Old Old
Inside Inside Inside Outside
4) "Answer" command? Changes Same Same Same
5) ARPANET name space 1 per 1 per 1 per 1 per
use? FWDR FWDR user user
Goals:
1) Software Change Bad Bad Good Good
2) User Acceptance Bad Good Good Poor
3) Future Compatibility Bad Poor Poor Fair
4) Transition Software Fair Good Bad Good
Conclusions:
Solution D is recommended.
Only solution D is based on the use of strictly "outside"
information. Please note that the existing ARPANET message
DELIVERY system is based strictly on the use of "outside"
information only. Also note that the problems that keep coming up
in ARPANET message processing & composition programs have to do
with the different possibilities for syntax (and semanitcs) of the
"inside" information. This is a major advantage of solution D.
Postel [page 9]
RFC 754 6 April 1979
Out-of-Net Host Addresses for Mail
Please note that the syntax NET-USER@FWDR in the examples is not
the only form that could be used. Any of the following (or even
others) would be fine:
Net-User@FWDR User-Net@FWDR
Net/User@FWDR User/Net@FWDR
Net.User@FWDR User.Net@FWDR
Net.and.User@FWDR User.on.Net@FWDR
Postel [page 10]