some users are unable to contact exchange servers using Outlook. OWA, Activesync is OK

Hi Experts,

I have a few clients [5 users] that cannot connect to Exchange server from any laptop or desktop with OUTLOOK.Everything else seems to be fine; Lync, IPhone, webmail.

Users are hosted on different DBs, and they use outlook 2010 latest SP and Outlook 2013

Our exchange environment as per below:

2 CAS/HUB servers for each site. Windows 2008 R2 OS. Exchange 2010 SP3 version.

2MBX/UM servers for each site. Windows 2008 R2 OS. Exchange 2010 SP3 version.

The rest of users are connecting to outlook without any issues.

Troubleshooting steps taken so far:

At server level:

.       Check the status of DAGs, DBs, replication, etc. no issues

.       Check of the problematic mailboxes. no issues

.       no obvious errors from app/sys logs

At client level

•      user gets her emails  from iPhone and webmail no problem
•      Created new profile  but I get the same error message:
•      You must connect to Microsoft Exchange with the current profile before you can synchronize your folders with your outlook data file (.ost).
•      I logged in as me I can use outlook without any issue.
•      I gave her new laptop loaner she gets the same message when we start outlook.

•      Close outlook, and  Lync client. Go to task manager and make sure to kill outlook/communicator/UCMapi.ex *32 processes
•      From windows explorer, find any OST file associated to this user, take a backup to an alternate folder, then delete all OST files of user and any other user.
•      From control panel, delete all outlook profiles.
•      Go to command prompt, run cmd as elevate admin rights, and type gpupdate/force. Once this task is completed, enter N and do not reboot the laptop
•      Create a new outlook profile for user.

Any ideas?
Jerry SeinfieldAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
Try removing cached exchange mode for Outlook and try again. Also launch Outlook and right click on the Outlook icon in the system tray and select "Connection Status" check to see what servers they are authenticating to.

You might also want to try a new Windows User Profile.

Stupid question, which I didn't see directly addressed in your original post... do the affected users have MAPI access enabled on their mailboxes?

Sorry, but sometimes a reboot is all that is needed to fix a complex problem. :)
Jerry SeinfieldAuthor Commented:
finally we had an issue with IPV6 where some users were unable to contact the CAS server, issue resolved, thanks everyone

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Jerry SeinfieldAuthor Commented:
all suggestions made did not work, further investigation showed there was an issue with the CAS server and IPV6 enabled. After disabling IPV6 and flush DNS, issue resolved
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