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On a Microsoft Exchange Server 2007 Service Pack 1 (SP1) server that has the Client Access server (CAS) role, you may notice high CPU usage when the IMAP4 service is running. As a result, the client computer may not be able access the server, or it may get a slow response from the server.
This issue occurs because the Microsoft.Exchange.Imap4.exe process falls into an inefficient loop when Exchange Server 2007 processes some search operations.
To resolve this problem, install Update Rollup 7 for Exchange 2007 Service Pack 1.
For more information about Update Rollup 7 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic: