The IMCDATAQUEUE.DAT file in Exchange manages the state of each message queued up in Exchange as it passes through the IMS (Internet Mail Service). If this file becomes damaged, or if another program changes its permissions or inhibits changes to it, Exchange can exhibit bizarre, unpredictable behavior that is extremely difficult to diagnose.
Some of the common symptoms of problems with the QUEUE.DAT file are:
- Some messages get delivered repeatedly, even up to hundreds of times (both in and out).
- The Exchange service does not start and a spurious error is logged.
- Messages do not come in or out at all.
- CPU utilization for the server is above normal, or peaking at 100%, with the Exchange service being the main culprit.
The first course of action should be to check if a virus scanner or other program is blocking QUEUE.DAT in some fashion. If the queue is exceptionally large, a virus scanner may take a long time to plow through it, and during that time no changes to the file can be made, which can throw Exchange out of sync. (If you do have such a virus scanner, place QUEUE.DAT into its exclusion file.) Another program that can cause such a problem is a defragmenter (such as Raxco PerfectDisk or Executive Software's Diskeeper), which also needs to lock files for exclusive access when defragmenting them.
If there are no obvious problems of this nature, the file may simply be damaged and should be deleted. Stop the Exchange service before deleting the file. This may cause some messages to be sent twice, but if you have already experienced problems of the variety where messages are sent hundreds of times, this won't be a big price to pay.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter. Check out his Windows 2000 blog for his latest advice and musings on the world of Windows network administrators – please share your thoughts as well!