MAPI-based tasks do not work with virus API anti-virus software running on the Exchange Server computer

When you attempt to perform Messaging Application Programming Interface (MAPI) operations on an Exchange Server computer that is running an anti-virus software that is based on anti-virus application programming interface (API), you may receive a MAPI time-out error message.

These MAPI operations include the following:

• Performance of an offline folder synchronization (.ost synchronization).
  
  When an .ost synchronization does not work, if you view the .ost synchronization log it includes the following error message:

  12:51:31 Error synchronizing folder
  12:51:31 [80004005-501-0-550]
  12:51:31 The client operation failed.
  12:51:31 Microsoft Exchange Server Information Store
  						

  In addition, in Microsoft Outlook 2002, the following error message is displayed during the synchronization:
  Task 'Microsoft Exchange Server' reported error (0x00040820): Errors in background synchronization.
  
  In most cases, further information is available in a synchronization log in the Deleted items folder.
• Performance of a Move Mailbox operation.
• Use of the Microsoft Exchange Mailbox Merge program (Exmerge).
• Export to a personal folder file (.pst file).

When you move messages from a mailbox to a .pst file, you may receive the following error message:

This issue can occur if these MAPI operations gain access to a large number of attachments that have not been scanned by using the current virus signatures. The MAPI operations do not determine that the attachments are waiting to be scanned; therefore a time-out error message is displayed if the scans are not completed to make the attachments available to the MAPI request in a sufficient amount of time.

NOTE: Any Microsoft Outlook user or any third-party package (for example a backup package) that needs to access messages or attachments may encounter this problem if the anti-virus software package uses VAPI 1.0.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
To work around this issue, make sure that the BackgroundScanning value is enabled and increase the OpenRetryDelay value from the default setting.

NOTE: These procedures reduce, but may not eliminate, the number of error messages that are displayed during MAPI operations.

To enable the BackgroundScanning value, you need to edit the registry:

1. Start Registry Editor (Regedt32.exe).
2. Locate the BackgroundScanning value under the following key in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\VirusScan
3. If the value is set to 0, change the value to 1; double-click the entry and change the value to 1 Binary.
4. Quit Registry Editor.

The BackgroundScanning process begins one minute after you change this key.

After you enable the BackgroundScanning value, Microsoft recommends that you allow approximately one hour to pass for each gigabyte (GB) of attachments that is stored in your private information store before you perform a MAPI operation, to ensure that all attachments have been scanned. After that amount of time, MAPI error messages are greatly reduced or may be eliminated.

To increase the OpenRetryDelay value:

1. Start Registry Editor (Regedt32.exe).
2. Locate the OpenRetryDelay value under the following key in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\VirusScan
3. On the Edit menu, click DWORD, type 5000, and then click OK (This is a decimal entry).
4. Quit Registry Editor.

If the OpenRetryDelay value does not exist, create it:

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\VirusScan
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value Name: OpenRetryDelay
   Data Type: REG_DWORD
   Radix: Decimal
   Value: 5000
4. Quit Registry Editor.

Attachments are scanned when they are sent or received by the Exchange Server computer if the anti-virus API is enabled. However, those attachments that are already present when you install the anti-virus software or update the virus signature file need to be rescanned when an operation gains access to those attachments, unless the BackgroundScanning process has scanned those attachments. This ensures that those attachments have been checked with the latest virus signature file. The BackgroundScanning process begins a full scan of all attachments in the information store when virus signatures change or the vendor of the virus software changes.

The BackgroundScanning process is disabled by default on many types of third-party anti-virus software.

In addition, the OpenRetryDelay value that the anti-virus software uses determines the time interval, in milliseconds, that the information store pauses before the information store attempts to reopen attachments that are being scanned when they are requested by the client. If the attachment is not scanned and made available to the MAPI request within this time interval, a time-out error message is displayed.

By default, the information store uses a setting of 500 milliseconds (msec), or one-half of a second, unless otherwise specified in the registry.

All attachments are rescanned after virus signatures are updated. Before an operation can gain access to these attachments, it is important that you plan a signature update to occur during off-peak hours. This allows time for the attachments to be scanned and made available to MAPI operations. Due to the way that some anti-virus vendors update their product, stop and restart the information store after a virus signature upgrade to re-initiate the background scanning task.