Proper setting for smtp_from in new trac instance?

[Jason L Tibbitts III]

Perhaps I missed it but I didn't see any kind of guide to setting up a
new fedorahosted trac instance so I copied from one other trac where I
have privileges.  That trac has smtp_from set to trac at fedorahosted.org.

The problem with this is that some hosts appear to do SMTP callouts and
reject messages sent with that setting:

May 29 04:42:36 hosted03.vpn.fedoraproject.org postfix/smtpd[17813]:
NOQUEUE: reject: RCPT from XXX: 550 5.1.1 <trac at fedorahosted.org>:
Recipient address rejected: User unknown in local recipient table;
from=<> to=<trac at fedorahosted.org> proto=SMTP helo=XXX

infradead.org is one such host that does this, but it is not the only
one.

It appears that several trac instances are using this setting.  Should I
be using something else or is it possible to get an alias from trac@ to
nobody@ set up so that this will work?

 - J<