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.


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.

  • Egad-- a shot in the dark. Glad I could help. – Evan Anderson Jun 23 '09 at 14:59
  • Nice shot in the dark! :) – squillman Jun 23 '09 at 15:21
  • To prevent this from happening again you might want to check out linkServerPulse, a service that monitors your Exchange and sends you a text message and an email if the disk space runs low or the server goes down. – Claus Christensen Aug 18 '13 at 6:50

What's your domain name?

  • Has your domain expired?
  • Can external dns resolve your MX records properly?
  • Change in firewall config possibly?
  • No, the domain appears valid. The external DNS tests we performed seemed to indicate that everything was fine. Firewall changes have not been made for several weeks. A little more information is available in the question, pertaining to system resources. – Michael Todd Jun 23 '09 at 14:37
  • Oh, and the domain is ccrfcd.org. – Michael Todd Jun 23 '09 at 14:49

If there has been no firewall change then there is likely an issue with your MX records. Use nslookup and check an external DNS server to see what they resolve to. You can also try sending yourself an email by telneting into the server.

  • Which did not work due to a "452 Insufficient system resource error" (even though we have plenty of disk space and have recently rebooted the server). Any thoughts? – Michael Todd Jun 23 '09 at 14:40

Just to check - how is external mail coming in? Direct delivery to the server, via some av/spam filter gateway or are you pulling mail down using a connector etc?

If mail is delivered direct to the server then definitely look at DNS/MX resolution issues and firewall changes which may be blocking delivery. You can do a quick test by trying to telnet to your server on port 25 from a machine external to your network.

If you route via another gateway service for filtering as many people now do you need to check whether they are queueing up your mail as they can't connect to your server.

Check the logs for any errors.

  • We are using a connector to a front-edge server. Telnet to port 25 appears to work (internally, anyway; I'd have to walk across the street to test external, and probably will be doing so soon). – Michael Todd Jun 23 '09 at 14:41

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