Exchange Back Pressure!

by Matthew Pusey on December 2, 2010

This is really annoying if you don’t know where to look. So, if you had this issue, all email services started, internal mail works fine, exchange works fine, spamsoap(3rd party anti-spam provider and a damn good one!) can connect to the server and you see messages coming through spamsoap but never hitting the mail server.. I assumed Spam Soap was the issue. Highly untrue..

If you go to the message audit in Spam Soap, then click on the messages it gives you valuable information

2010-12-02 09:04:27 EST Recipient Disposition: [250 Deferred; Mode: normal; Queued: yes; Frontend TLS: yes]
2010-12-02 09:04:44 EST Detail: first attempt failure: 452 validating sender: 4.3.1 insufficient system resources


Interesting.. insufficient resources.. I was actually excited for a second because this might need a reboot and I could update VMWare tools in the process!  I checked the server.. plenty of CPU and memory was at like 92%.. I didn’t really think that was the issue.  I am let down.. naturally I google the error, Back Pressure.. Oh yeah!! In Exchange 2007, 2010, the Hub Transport server monitors the disk space to prevent the drive where the Exchange DB is from going to 0 disk space.. awesome idea! The server hag 2.55GB free.. I deleted some install files.. 8GB free.. all my emails immediately were delivered.. awesome..

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