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Consider the following scenario:

  • You use Microsoft Outlook or you use Microsoft Outlook Web Access (OWA) to log on to a mailbox in a Microsoft Exchange Server 2010 environment.

  • You enable the Calendar logging feature.

  • You use Internet Message Access Protocol version 4 (IMAP4) to access the contacts folder in the mailbox.

  • At the same time, other users log on to the mailbox.

In this scenario, the other users who log on to the mailbox by using Outlook or OWA experience a decrease in performance. For example, an hourglass icon appears for several seconds in Outlook. Or, OWA remains stuck in the refreshing state.

Note The Versions folder item counts in the mailbox is very high (several million) when you run the following command to query the count:

Get-MailboxFolderStatistics -Identity <Your test mailbox> -Folderscope RecoverableItems | ft name, ItemsInFolder -autosize


This issue occurs because the IMAP4 service triggers an unnecessary copy on write (COW) action when it accesses the contacts item. Then, a recoverable item is created in the dumpster versions folder. Therefore, performance decreases when too many unnecessary recoverable items are in the dumpster versions folder.


To resolve this issue, install the following update rollup:

2579150 Description of Update Rollup 4 for Exchange Server 2010 Service Pack 1


To work around this issue, use one or more of the following methods:

  1. Disable the IMAP4 protocol.

  2. Change to another access method such as Exchange Web Services (EWS).

  3. Disable the Calendar logging feature when you run the following command:

    Set-Mailbox -Identity < user- identity > -CalendarVersionStoreDisabled:$true


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

More Information

For more information about a similar issue, click the following article number to view the article in the Microsoft Knowledge Base:

2463798 Performance in Outlook or in OWA decreases when you use IMAP4 to access the calendar folder in an Exchange Server 2010 SP1 environment

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