When a user’s alias and SamAccountNameparameter (also known as the pre-Windows 2000 user account or group name) are different, the user can't log on to a POP/IMAP account by using NTLM authentication in Exchange Server 2013.
This issue occurs because the NTLM authentication method logon tries to locate the user by SamAccountName, where the user name is set to the user's alias.
Exchange Server 2013
To resolve this issue, install Cumulative Update 21 for Exchange Server 2013 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.
Learn about the terminology that Microsoft uses to describe software updates.