Outlook keep prompted for Password every time outlook starts

Dears,

i setup single Exchange 2013 (CAS/Mailbox) server,, and i used Outlook 2013 in Joined Domain machines, the profile configured automatically but once access the outlook every time i got password prompt then i type and could access

this is Exchange 2013 CU5 , INTENRALClient authentication is set to NTLM ,  no external Outlook anywhere configured,  IIS authentication is set to basic, ntlm, negotiate..

i tested in test lab and worked charm,, but i don't know what is the issue in Production server

your help is appreciated