Consider the following scenario:
- You have a mixed Microsoft Exchange Server 2007 and Microsoft Exchange Server 2003 environment.
- You have Exchange Server 2007 Service Pack 3 Update Rollup 2, 3, 4 or 5 installed on Exchange Server 2007 servers.
- You use an Exchange Server 2007 Client Access server to proxy requests for Exchange Server 2003 mailbox servers.
- Users try to access the mailboxes that are hosted on the Exchange Server 2003 servers by using Internet Message Access Protocol 4 (IMAP4) clients.
This issue occurs because of a deadlock when the Client Access server manages and releases the IMAP4 session and the proxy session.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.