Smarthost Failover - WAS RE: [Mimedefang] SMTP mailertable question

[Kris Deugau]

"Cormack, Ken" wrote:
> Kris Deugau wrote:
> > At a guess, enclosing hostnames in []'s would eliminate that- if
> > you're relaying mail for something, for instance, you may want to
> > explicitly specify a destination hostname rather than allowing
> > sendmail to try an MX lookup on that name.
> 
> Enclosing the hostnames in brackets would not work.  The function of
> the brackets is to signify to sendmail that the enclosed entity is a
> litteral IP address not requiring lookups of any kind (as opposed to
> a "name" of some sort, against which MX and/or PTR lookups are
> needed.)  This is mentioned in other contexts, in the sendmail
> litterature.

Hmmm.  I mentioned it because []'s are used in the mailertable to tell
sendmail "Don't look up an MX for this hostname, just assume that that
hostname accepts incoming SMTP on port 25".  It works just fine with
hostnames there.  It still does a lookup for the A record so it can
connect to that host, but it doesn't do any further DNS checks.

For instance, in the mailertable on the hosting server here, I have
lines like:

domain.com	esmtp:[domain.com]

They host their own mail, but our hosting server is a backup MX, and
leaving out the brackets may cause sendmail to go into a loop trying to
deliver to itself.  :/  (I think it actually did so once.)

I may try some testing to see what happens.

-kgd
-- 
"Sendmail administration is not black magic.  There are legitimate
technical reasons why it requires the sacrificing of a live chicken."
   - Unknown