Sun Microsystems Sun Workstation 100U System Manager's Manual page 325

SENDMAIL
10
A nonuniform address space implies that a path will be specified in aU addresses, either
explicitly (as part of the address) or implicitly (as with implied forwarding to gateways). This
restriction has the unpleasant effect of making replying to mess3les exceedingly dillicult, since
there is no one "address" for any person, but only a way to get there from wherever you are.
Interfacing to mail programs that were not initially intended to be applied in an internet
environment has been amazingly successful, and has reduced the job to a manageable task.
Sendmail has knowledge of a few difficult environments built in. It generates
ARP ANET FTP /SMTP compatible error messages (prepended with three-digit numbers
[Neigus73, Postel74, Postel82)) as necessary, optionally generates UNIX-style "From" lines on
the front of messages for some mailers, and knows how to parse the same lines on input. Also,
error handling has an option customized for BerkNet.
The decision to avoid doing any type of delivery where possible (even, or perhaps espe-
cially, local delivery) has turned out to be a good idea. Even with local delivery, there are
issues of the location of the mailbox, the format of the mailbox, the locking protocol used,
etc., that are best decided by other programs. One surprisingly major annoyance in many
internet mailers is that the location and format of local mail is built in. The feeling seems to
be that local mail is so common that it should be efficient. This feeling is not bom out by our
experience; on the contrary, the location and format of mailboxes seems to vary widely Irom
system to system.
The ability to automatically generate a response to incoming mail (by forwarding mail to
a program) seems useful ("I am on vacation until late August .... ") but can create problems
such as forwarding loops (two people on vacation whose programs send notes back and forth,
for instance) if these programs are not well written. A program could be written to do stan-
dard tasks correctly, but this would solve the general case.
It might
be
desirable to implement some form of load limiting. I am unaware 01 any
mail system that addresses this problem, nor am I aware of any reasonable solution at this
time.
The configuration file is currently practically inscrutable; considerable convenience could
be realized with a higher-level format.
It seems clear that common protocols will
be
changing soon to accommodate changing
requirements and environments. These changes will include modifications to the message
header (e.g., [NBS80)) or to the body of the message itsell (such as lor multimedia messages
[Postel80)). Experience indicates that these changes should be relatively trivial to integrate
into the existing system.
In tightly coupled environments, it would be nice to have a name server such as Grap-
vine [Birre1l82] integrated into the mail system. This would allow a site such as "Berkeley" to
appear as a single host, rather than as a collection 01 hosts, and would allow people to move
transparently among machines without having to change their addresses. Such a facility
would require an automatically updated database and some method of resolving con8icts.
Ideally this would be effective even without all hosts being under a single management. How-
ever, it is not clear whether this feature should be integrated into the aliasing facility or
should be considered a "value added" feature outside 8endmail itself.
As a more interesting case, the CSNET name server [Solomon8!) provides an facility
that goes beyond a single tightly-coupled environment. Such a lacility would normally exist
outside 01 8endmail however.
ACKNOWLEDGEMENTS
Thanks are due to Kurt Shoens for his continual cheerlul assistance and good advice, Bill
Joy for pointing me in the correct direction (over and over), and Mark Horton lor more advice,
prodding, and many of the good ideas. Kurt and Eric Schmidt are to be credited lor usiD,
delivermail as a server Cor their programs (MtJil and BerkNet respectively) before any sane person
should have, and making the necessary modifications promptly and happily. Eric gave me
Version 4.1
DRAFT
Last Mod 8/20/83