Network Working Group D. Crocker (UCLA-NMC)
Request For Comment: #539 J. Postel (UCLA-NMC)
NIC 17644 July 9, 1973
Thoughts on the Mail Protocol Proposed in RFC 524
Generally, we feel that the protocol is extremely rich. We also feel
that there are some minor and some major problems.
The minor points first:
1. <CA> and <CA2> are not explained until the formal syntax. It
would be more convenient, if they were explained sooner.
2. The Proposed <CA2> is a bad thing, since it is the Telnet Go-
Ahead, which should not be used by higher level protocols.
3. The default SIGNATURE should be the sign-on or ident of the
4. The Disposition INTERRUPT would be more useful if it had
author/clerk-assigned "levels". Currently mail would be either
urgent or not. With levels (say 1 to 10), the sender could rate the
degree of urgency.
There would be no precise defined meaning to any of these
levels, merely the opportunity for a subjective evaluation by
the sender. The receiver (process or person) may do whatever
they wish with the information.
A user could thereby direct a receiving process to notify him
immediately of Priority 5 or higher Short mail or any Priority
10 mail immediately, but defer notification of any other mail.
(Length is discussed later in this note.)
5. Also, we would like the word, "INTERRUPT", to be changed to
URGENT or PRIORITY
6. In keeping with offering the sender the opportunity to 'rate' his
mail, we would like to allow him the chance to warn the receiver of
the size of the mail. This could be a byte count and/or an
imprecise SHORT/MEDIUM/LONG. Again, the receiver may use this
information as he/it sees fit.
7. The ID command seems confusing.
If I am a clerk and sending to someone on another host, that
host may ask me to 'prove' my identity by using an ID. How can
the Sigma-7 at UCLA-NMC know WHITE's id? He does not have one on
the Sigma, but certainly should be able to send mail to us
8. How do ACK's, Progress Reports, or Replies work when there is no
Reference Serial number?
9. Please include the distinction between Static and Dynamic
attributes as part of the formal syntax.
10. Though hosts must be allowed to require a login, before they
will accept mail, would like the Protocol document to reflect a
negative attitude towards such a requirement.
11. In describing defaults, relatively cryptic phrases such as
"Author to the Clerk" are sometimes used. Please be a bit more
12. The sender is required to send Static, Dynamic, and then
This requires receiving hosts to buffer the contents before
passing them on to the appropriate recipient. (In fact, before
finding out whether it can/will accept the mail.)
The order should be: Dynamic, Optional, Static.
By requiring the sending host to transmit the dynamic and
optional attributes first, the receiving host can also reroute
mail based upon its Priority and Length.
Now for the hairier problems:
1. We would like to make a strong statement in favor of the
unified-access (one selector process with one listening socket)
approach. However, since it does not exist, yet:
The Mail Protocol should NOT be a subsystem of FTP. The Mail
Protocol USES the File Transfer Protocol, the same as RJE uses
FTP. We therefore suggest the use of the RJE model.
This unfortunately opens up the issue of logging in, to send
mail. The advantage of having FTP have a MAIL command is that it
defines a class of data transfer which many hosts will allow for
free, while maintaining control over other, 'normal' file
The solution should be the same as that currently used by RJE.
2. The FORWARD function allows a site to receive and hold mail
during and/or, until a transfer request is received from the
'recipient' at another host.
This action takes place AFTER receipt of the mail, so we would
like to suggest a command for "Rerouting" mail just PRIOR to its
This allows a receiving host to refuse a given piece of mail,
but suggest an alternate receiver. This would be useful if the
recipient were using another host for a while, or if the
recipient didn't want to rack up storage charges at the first
Three variation can occur, one of which will require a special
MP reply code:
Automatic forwarding: Accept the mail and then
automatically transfer it to the user's alternate mailbox.
This could be classed as a user "feature" and would
not be part of the protocol. However, it would be quite
Automatic forwarding with copy held: The same as the first
case, but the transferring server keeps a copy of the mail.
Rerouting without accepting: The mail is never accepted
from the sender. The sender is, however, informed of an
The Rerouting information would be in reply to a
476 <recipient> IS AT <pathname>
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