You have a computer that is running the Microsoft Exchange Server 2007 CAS role.
A user connects to the CAS server by using an IMAP4 client.
The IMAP4 user tries to open a folder that contains many items. For example, there are more than 50000 items in the folder.
In this scenario, the Microsoft Exchange IMAP4.exe process occupies 100% CPU usage on the CAS server for a long time. Therefore, the CAS server becomes slow or not responding to other users.
This problem is caused by a lack of performance when the Microsoft Exchange IMAP4 service process too many items.
To resolve this problem, install the following update rollup:
972076 Description of Update Rollup 2 for Exchange Server 2007 Service Pack 2
After you apply this update, you can add a key named MaxFolderItemCount in the Microsoft.Exchange.Imap4.exe.config file. After an Exchange administrator apply this update, the Exchange administrator can add a key namedMaxFolderItemCount in the Microsoft.Exchange.Imap4.exe.config file to set the expected maximum number. After that, if a user tries to open a folder whose item count exceeds the maximum item count that the Exchange administrator have set in the MaxFolderItemCount key, the Exchange Administrator will receive the following 2103 warning message to find out whose mailbox cause the problem:
Event ID: 2103 Event Type: Warning Event Source: MSExchangeIMAP4 Description: User <legacyExchangeDN of the logon user> is trying to open folder <Folder name> in mailbox <legacyExchangeDN of the mailbox mailbox user>, but the items in this folder have exceeded the maximum allowed number: <number you set>. The current number of items is: <real number>.
A sample of Microsoft.Exchange.Imap4.exe.config is as following:
Note You have to restart the Microsoft Exchange IMAP4 service for the change to take effect. Use of the MaxFolderItemCount does not prevent IMAP users from accessing folders that exceed the MaxFolderItemCount value.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.