VSAPI-based antivirus software causes delayed response in an Exchange Server 2010 environment

Consider the following scenario:

• You use Microsoft Exchange Virus Scanning API (VSAPI)-based software in a Microsoft Exchange Server 2010 environment.
• A user’s mailbox that is protected by the antivirus software contains multiple messages.
• The user performs a certain operation on the mailbox to connect to a Mailbox server. For example, the user enables the AutoPreview feature in order to view multiple messages by using Microsoft Outlook in online mode.

In this scenario, there is a long delayed response from the Mailbox server. Additionally, this issue may prevent new clients from connecting to the Exchange server, or it may trigger a failover of databases to standby servers.

This issue occurs because the operation that the user performed triggers a property promotion that triggers virus scanning requests for each message item. When there are many items in the virus scanning queue, all remote procedure call (RPC) connections to the Mailbox server are exhausted as new clients wait for the virus scanning operation to finish. Therefore, the Mailbox server cannot respond to any RPC requests. Then, monitoring detects that the Exchange server is unresponsive and initiates a failover.

To resolve this issue, install the following update rollup:

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

For more information about how to enable the AutoPreview feature, go to the following Microsoft website:For more information about the property promotion, go to the following Microsoft website: