IMAP4 clients cannot log on to Exchange Server 2003 servers when the Exchange Server 2010 Client Access server is used to handle proxy requests

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Symptoms

Consider the following scenario:

You have a mixed Microsoft Exchange Server 2010 and Microsoft Exchange Server 2003 environment.
You configure an Exchange Server 2010 Client Access server to handle proxy requests for Exchange Server 2003 servers.
The Exchange Server 2003 servers have the Chinese version of Exchange Server 2003 installed.
Users try to access the mailboxes that are hosted on the Exchange Server 2003 servers by using Internet Message Access Protocol 4 (IMAP4) clients, such as Outlook Express.

In this scenario, the users cannot log on to the Exchange Server 2003 servers. Additionally, the users receive the following error message:

The server has rejected your login. Please verify that your user name and password are correct.

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Cause

This issue occurs because the Exchange Server 2010 Client Access server incorrectly handles the namespace string that is returned from the Chinese version of Exchange Server 2003. The returned namespace string does not have the required quotation marks. Therefore, the logon process fails when the Exchange Server 2010 Client Access server checks the text pattern.

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