Exchange 2007 - no inbound e-mail. Any ideas why?

We are running Exchange 2007 and have been doing so for a few years now with only occasional issues. This morning, however, we are not receiving any inbound (external) e-mail. Internally sent e-mail seems to be fine and we can send e-mail out, but nothing is coming in from any domain.

We've rebooted the mail server as well as our domain controller and that seems to have had no effect.

Any ideas about what we should look for to resolve this?

UPDATE: I telnetted into the server and found that the server responds with 452 Insufficient system resources when I perform the MAIL FROM command. We appear to have plenty of disk space and have recently rebooted so memory isn't an issue. Still not working, though.

FURTHER UPDATE: We disabled the Back Pressure threshold as one poster suggested and we are no longer getting the 452 error, but we're still not receiving any e-mails. Perhaps things are backed up at the moment; I'll check again in a little bit to see if things are moving along.

Solution 1:

Do you have at least 4GB disk space free on the volume where the SMTP virtual server is storing its SMTP queue?

If not, you can move it with this procedure: http://technet.microsoft.com/en-us/library/bb125177.aspx

Edit: You're probably having a backpressure situation-- I didn't even stop and think about that. Ugh! Backpressure got a lot better after one of the post SP1 rollups, but I can't tell you which. Your event log will tell you if you're having a backpressure event, though.

Solution 2:

What's your domain name?

• Has your domain expired?
• Can external dns resolve your MX records properly?
• Change in firewall config possibly?