debathena-msmtp-mta should do local delivery for local users

[andersk]

Currently debathena-msmtp-mta will send all mail through outgoing.mit.edu, including local mail. For example, sudo alert mails to root will go to root@…. We should figure out how to make it do local delivery for members of the nss-local-users group.

[geofft]

I don't know if there's a good way to address this. We'd have to add our own code for putting mail in /var/mail or wherever else we think "local delivery" should mean. As far as I can tell, the other lightweight mail-transport-agents all have the same bug, so there isn't standard code that we can adopt.

If you want local mail delivery, you should set up exim4-daemon-light (which appears to be Debian's default MTA when you need one for some reason) or something similar, in my opinion... so I'd like to declare this out of scope for debathena-msmtp-mta.

What we could do, however, is respect an aliases-like file that maps local users to public e-mail addresses (which we usually expect to be @mit.edu), and have a default rule for unknown users. For my laptop, I want mail to go to geofft@, not to /var/mail/root which I have to check with "sudo pine" or something. For, e.g., scripts' servers, I want all unknown mail to go to scripts-root@ rather than to a local mail spool.