Re: [PLUG] Backup MX Question

["Michael C. Toren" <mct@toren.net>]

On Fri, Jun 02, 2006 at 09:48:06AM -0400, Michael Bevilacqua wrote:
> I recently setup a new backup MX for a large volume mailhost and found
> the backup MX host queuing thousands of spam.

It's extremely common for a secondary MX to be hit harder by spam than
the primary.  Many spammers will attempt to deliver message directly
to the secondary, even when the primary is up and running.  Worse, as
you've seen, the secondary can get bogged down trying to delivery bounce
messages generated when the primary won't accept a given message, for
example if the destination address is unknown.  If this is in fact what
you're seeing, and these are the types of messages in your queue, then
doing this:

> As per the sendmail documentation I disabled double bounces using:
> 
> define(`confDOUBLE_BOUNCE_ADDRESS',`')dnl

won't help to reduce your queue.  The "double bounce address" is where
notifications should be sent when a bounce messages in your queue was
undeliverable.  When not discarded, these messages are normally directed
to the local postmaster mailbox.

I'm guessing the problem you're having, though, is not who to notify when
bounce messages are undeliverable, but rather dealing with the quantity
of bounce messages in the first place.  While there are tricks for coping
with that (such as greylisting, or keeping a cache of valid usernames the
primary will accept mail for on the secondary so that delivery attempts
to invalid users may be rejected at SMTP time), there's no silver bullet.
Running a mail infrastructure requires a good deal of resources these
days.

-mct
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