Sometimes, the error messages that we get are absolutely misleading.  This is one of those cases where you get called to a server for a mail problem and end up wasting a couple of hours on a problem that could have taken mere minutes to fix.

The symptoms are pretty simple.  In this case, the customer is using the POP3 Connector and is no longer receiving emails.  This problem can occur in a number of scenarios with the same fix.  the event log shows this error:

An error occurred while delivering mail to ’someguy@someplace.com’ on the SMTP server ‘localhost’. The error code was 0×800ccc6c. Verify that the mailbox exists and that the Exchange receive connectors are configured properly.

I’ve had this problem but with different event logs as well, so if you are getting some weird things, this is definitely something to look into before you so do anything else.  Both times, the problem was low disk space on the system partition.

That’s right!  low disk space.  First time I came across this problem, the server had about 55mb left so it was a no brainer.  But this time, there was 1.86GB left so I figured I’d free up some space after I had resolved the email problem.  It turns out that there should always be at least 2GB of free space for exchange to work properly.

I started to move a 14gb folder (using Teracopy of course..) to another partition and, magically, emails started pouring in after a few minutes.