Archive for October, 2008
So I think I’ve finally come down to nailing what in the world was causing some emails to be randomly rejected after implementing ZoneEdit’s backup MX service. Now this post may be invalid if my understanding of greylisting is flawed but let me play it out. So someone sends us a email, the email is greylisted and bounced back to their server to be resent. The server says “Ok let me try this other MX”. It sends to the other MX which is zoneedit’s backup MX service.
Now here is the rub. ZoneEdit’s backup MX also does it’s own form of spam scanning which you cannot edit. It will reject messages that do not match the hostname. I see a lot of mail come in where the Client host has a active directory name like mailserver.local. So the secondary MX rejects it to the original sender with a 550 Client host rejected: cannot find your hostname. That secondary MX doesn’t even try and send me the message.
I also saw the message on the main xwall page about greylisting and zoneedit, which sort of pointed out to my ah HA! moment. So it either comes down to not using greylisting or dropping the secondary MX.