You may receive duplicate e-mail messages after a CCR cluster fails over unexpectedly in Exchange Server 2007

In Microsoft Exchange Server 2007, a cluster continuous replication (CCR) cluster fails over unexpectedly. After this occurs, you may receive duplicate e-mail messages.

This behavior occurs if the following conditions are true:

• You use Microsoft Office Outlook 2007 or Microsoft Office Outlook 2003 in Cached Exchange Mode.
• The transport dumpster is enabled on the hub transport server.
• The cluster failover is unexpected. For example, the active node is turned off.

Notes

• Duplicates occur only for e-mail messages that were delivered to the mailbox one or two minutes before the failover to the passive node occurred. E-mail messages that were delivered much earlier are not duplicated.
• This behavior does not occur in Microsoft Outlook 2000 and in Microsoft Outlook 2002. These versions of Outlook do not use Cached Exchange Mode.

This behavior occurs because the Exchange Server 2007 transport server redelivers e-mail messages that are in the transport dumpster when the transport dumpster is enabled. These e-mail messages are delivered as new messages that have a new PR_SOURCE_KEY property. Therefore, Outlook creates new items in the offline folders (.ost) file.

This behavior is by design.

Steps to reproduce the behavior

1. Set up an Exchange Server 2007 CCR cluster together with active/passive nodes.
2. Enable the transport dumpster on the hub transport server.
3. Connect Outlook 2007 in Cached Exchange Mode to the mailbox, and then send several e-mail messages to a logged-on user.
4. As soon as the e-mail messages are received, turn off the active node to simulate a lossy failover.
5. Do not exit Outlook 2007. Wait until Outlook 2007 resumes the connection to the server after the failover occurs.

After the transport dumpster redelivers the e-mail messages, Outlook displays duplicates of the messages that were received one or two minutes before the failover occurred.