Password prompts for outlook users.

i want to discuss my Problem of outlook users being prompted for passwords .

following is the configuration

AD site 1 : 2 malbox servers & 2 CAS servers running Exchange 2013 CU3
AD site 2 : 1 malbox server & 1 CAS server running Exchange 2013 CU3
Edge Transport Server: Exchange 2010 SP-3
users : Windows 7 / outlook 2010 & 13 Compliant with (http://technet.microsoft.com/library/ee681792%28v=office.15%29)

while outlook running perfectly suddenly a password pop up ofccures, even after providing credentials for 5 / 10 times are not authenticated.i googled it around & realized that this is a common issue after CU3 deployment. i ran Get-OutlookAnywhere and found my authentication setting are set as Basic, Negotiate and NTLM as described in URL-1 (written in the last) (i though i did not change my current setting as recommended in the page).

modified users outlook profile by unchecking “download shared folder” and set the authentication from negotiate to kerbros as mentioned in URL-2(mentioned in the last)although it worked for some days but again the same problem.

now i am thinking to upgrade my CAS servers only from CU3 to CU6 released in august earlier this year.

in my opinion any schema extention / prepareAD / PrepareDomain is not required in our case because i had CU3(please confirm).

URL-1:http://edsitonline.com/2013/11/29/outlook-usernamepassword-popups-after-exchange-2013-cu3-upgrade/

URL-2:https://social.technet.microsoft.com/Forums/office/en-US/11370f4d-b931-4338-8ab7-acc9e1a231e0/outlook-2013-asks-for-credentials-connecting-to-exchange-2010-multiple-times?forum=officeitpro

please also suggest if i can modify the authentication settings as mentioned in URL-1 because my only pain is to stop password prompts.