After you install any post-Exchange Server 5.5 Service Pack 3 (SP3) information store hotfix (between build 5.5.2652.68 and 5.5.2653.16), you may receive duplicate messages when the message was originally sent to you or to a distribution list that includes your mailbox.
Any information store fix after build 5.5.2652.68 has been changed to use the Internet ID globally unique identifier (GUID) instead of the Instance ID to track message duplication. The local delivery pointer is not initialized correctly after the modification.
To resolve this problem, obtain the latest service pack for Exchange Server 5.5. For additional information, click the following article number to view the article in the
Microsoft Knowledge Base:
XGEN: How to Obtain the Latest Exchange Server 5.5 Service Pack
Microsoft has confirmed that this is a problem in Microsoft Exchange Server version 5.5 SP3. This problem was first corrected in Exchange Server 5.5 Service Pack 4.