[LMStone]

Bill,

Your boss is clearly more tolerant of false positives than our clients are!

We do front-end conservative RBL checking to eliminate 80% - 90% of the mail flow from even hitting our Zimbra farm. We then run a bunch of other checks that catch (we believe) all of the garbage that the mismatched HELO/A record test would catch.

We do require a HELO of some sort FWIW, and a PTR record of some sort too, but since the mail flow actually hitting our Zimbra farm is 10% or so of what comes knocking on the front door, we have some spare cycles available to do more intensive spam checking on the servers themselves -- and we have had only two known false positives since we first deployed Zimbra back on version 4.0.3.

Hope that helps,
Mark