Exchange Server computers may encounter backlogs of items that are awaiting inbound conversion on the Internet Mail Service after you apply the fix from the following Microsoft Knowledge Base article:
Exchange Server 5.5 clients appear to hang when the information store queries the directory
The inbound conversion queue may not clear until the services are stopped and restarted. The services, particularly the information store, may take an abnormally long time to shut down or may stop responding (hang) while they are shutting down, whether or not the server has an Internet Mail Service configured.
The deadlock is caused by two threads that are waiting for two critical sections to complete. Thread 1 enters critsec A. Thread 2 enters critsec B. Before either thread releases the critical sections, thread 1 asks for critsec B and thread 2 asks for critsec A. This behavior was not a problem before the fix because the work being done before was all on the same thread, and locking order did not matter.
To resolve this problem, obtain the latest service pack for Exchange Server 5.5. For additional information, click the following article number to view the article in the
Microsoft Knowledge Base:
XGEN: How to Obtain the Latest Exchange Server 5.5 Service Pack
Microsoft has confirmed that this is a problem in Microsoft Exchange Server Store.exe builds 5.5.2653.7 through 5.5.2653.18. This problem was first corrected in Exchange Server 5.5 Service Pack 4.
To test this, import a lot of directory changes at the same time that you are modifying objects such as protocols, site addressing, or the Gateway Address Resolution Table (GWART). You must have many small changes being imported to catch this.