adrianTNT - 5:28 pm on Feb 2, 2009 (gmt 0)
I recommend this too, I had this issues few times with my dedicated servers. I cannot remember the file name to be edited, there is a file that contains the DNS names (usually 2 lines), and the DNS mentioned there ware offline, that caused the email connection to fail and emails got stuck in queue.
You may want to try additional or different DNS servers that your mail server uses. I seem to remember that we had a flood of mail problems some months back that was got fixed by changing the DNS entries.