Certain IMAP commands may cause the CPU usage to increase to 100 percent on an Exchange 2007 server that is running the Client Access Server (CAS) role

If a folder name for a Microsoft Exchange Server 2007 mailbox contains many asterisk characters (*) or percent characters (%), certain IMAP commands may cause the CPU usage to increase to 100 percent on an Exchange 2007 server that is running the Client Access Server (CAS) role. Additionally, if you use Windows Task Manager to verify the problem, you find that the Microsoft.Exchange.Imap4.exe process causes the high CPU usage.

When this problem occurs, the high CPU usage affects other users who access their mailboxes through the Exchange 2007 server that is running the CAS role. If you restart Microsoft Exchange IMAP4 service, the problem is resolved temporarily. However, the problem may occur again.

To resolve this problem, install Update Rollup 5 for Exchange Server 2007. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.