Question on reducing load on MailScanner machine

[Steve Freegard]

Christopher Fisk wrote:
> 
> The reason (Might not be a good one!) I have shied away from anything more than a backup MX which queues messages if the main MX server goes down is due to the logistics of keeping them both in sync with mail accounts.  I'm thinking I will have to move my account database to a third machine or just run it on one of the two I would have in place.
> 

Account database?  You mean valid/invalid users?; if so then
milter-ahead, smf-sav etc. can help you there by doing SMTP call-aheads
to your mail hub to verify recipients etc.

Nowadays queuing backup MXes are usually a bad idea as they act as spam
magnets (e.g. most bots attempt to connect directly to the backup MX
intentionally under the presumption that they aren't as well configured
as the primary); any mail you receive therefore requires full content
scans instead of being able to reject connections pre-DATA during the
SMTP transaction (via RBLs etc.).

Also backup MXes that don't verify recipients or where the primary does
SMTP time rejections will cause significant backscatter.

Cheers,
Steve.