Exchange 5.5sp4 behind Pix firewall. Pix SMTP filter called Mailguard is on by default. Known issue with Mailguard: breaks Microsoft’s authentication packets and won’t pass them through. I need to disable open relay and force authentication on emailclients. (we have to be able to relay for 4 domains we host – not my decision but I have to support it) Called Microsoft and they referred me to a fix up on port 25 for the Pix. The fix was applied and I was able to disable open relay, force authentication on mail clients, and send and receive fine. Then we got hit with 40,000+ spam attempts, which ended up stuck in outbound queue, which brought Exchange to a halt for 2 hours. We had to revert back Mailguard on for the Pix to spare the load on our mail server. Now I’m back to square 1. Currently Mailguard is on and open relay is enabled.
I would like to be able to turn off Mailguard (to allow MS authentication), disable open relay, force clients to authenticate and keep the spam attempts from reaching my Exchange server. The only apparent ways I can see accomplishing this is by firewall filtering or setting up an email server in front of our Exchange server.
Thoughts and ideas are greatly appreciated.
