There is a Microsoft Exchange server 2003 and Microsoft Exchange Server 2007 coexist environment.
You access an Exchange Server 2003 mailbox through an Exchange Server 2007 Client Access server (CAS) with the IMAP4 protocol.
You use the PLAIN authentication mechanism.
In this scenario, you cannot log on to the mailbox. Additionally, you receive the following error message:
"NO AUTHENTICATE failed"
When you use the PLAIN authentication mechanism, Exchange Server 2007 CAS passes the display name instead of the logon account name to the Exchange Server 2003 mailbox server. When this behavior occurs, authentication fails.
To fix this problem, apply the following update rollup:
972076 Description of Update Rollup 2 for Exchange Server 2007 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about the IMAP4 protocol and the PLAIN authentication mechanism, visit the following IETF Web sites: