IMAP clients that use NTLM authentication protocol are continually prompted for credentials in Exchange Server 2013

Assume that you have a Microsoft Exchange Client Access server that establishes sessions to a different Mailbox server in an Exchange Server 2013 environment. After you apply cumulative update 9 or cumulative update 10 for Exchange Server 2013, Internet Mail Access Protocol (IMAP) clients are repeatedly prompted for authentication credentials. 
This is a known issue in Exchange Server 2013.
To work around this issue, follow these steps to restart your IMAP services on the Exchange Server 2013 server:
  1. Disable the EnableGSSAPIAndNTLMAuth parameter.
  2. Run the Set-IMAPSettings -EnableGSSAPIAndNTLMAuth $false cmdlet.

To fix this issue, install Cumulative Update 11 or a later cumulative update for Exchange Server 2013.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Article ID: 3076376 - Last Review: 02/12/2016 00:44:00 - Revision: 2.0

Microsoft Exchange Server 2013 Enterprise, Microsoft Exchange Server 2013 Standard

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