Be prepared for your higher-numbered MXes to get hit harder with spam than your lower-numbered MXes. (By that, I'm referring to the priority numbers in the MX records in DNS, not by the names of the servers.)
In a number of spam discussions/presentations at LISA, it has been noted that spammers tend to go harder at the "backup" MXes because they believe those MXes tend to be less protected against spam than the primary MXes. I can say that my site's experience certainly goes along with that. The secondary MX for our domain handles far more incoming SMTP connections than the primary, but after the spam filtering happens the primary MX actually relays more mail to the inside network than the secondary - by a factor of four or five.
So, if I'm going to pick which MX to use first when new anti-spam techniques are ready to be rolled in to production, guess which one I'll do it on... ;-)
-----Original Message-----
Sent: Thursday, November 08, 2007 10:06 AM
Subject: RE: [SAGE] More Spam than I ever imagined...
It seems to me that you could simply add a second MX record for all of
your domains pointing to a second server, and add third, fourth, etc as
your load increases. You don't necessarily split them in half depending
on batch sending, but I assume that 51% of your spam is not ALL from the
same source....
Domain.com in MX mx1.domain.com
Domain.com in MX mx2.domain.com
...
And then on mx1 and mx2, you have the equivalent spam filterish sort of
things.
Scott Carlson