Secondary MX (was Re: [Mimedefang] What is the order of things that occur)

[David F. Skoll]

Chiming in...

If you are going to have a secondary MX machine, then it should have
knowledge of all local accounts on the primary MX machine, and this knowledge
should be accessible even if the primary is down.  That means some kind
of periodic synchronization of user lists from the primary to the
secondary.  Be aware that there may be windows in which the secondary
rejects a recipient the primary would have accepted, or vice-versa,
but if your synchronization interval is small enough, it's probably
an acceptable tradeoff.

md_check_against_smtp_server was *not* designed for a secondary to
check against a primary.  It was designed for people who use an
Internet-facing MIMEDefang box as a front-end to relay to their real
mail server.  In this situation, the real mail server can reasonably
be expected to be highly-available (and if it's down, then it's OK for
the MIMEDefang box to tempfail.)

Regards,

David.