I've spent a couple days searching for an answer but haven't had any luck.  I've tried several different users on different computer and I can't get Outlook to connect when adding a new user.  When adding the account it gets through establishing network connection and searching for user setting but won't log onto the mail server.  A prompt for username and password comes up but entering credentials doesn't help.  An error pops up after entering credentials, The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.  The exchange server is fully patched with latest updates, outlook clients are as well.

What version of exchange you are running ?

Is it with exchange 2010 & 2013 coexistence?

Hi,

According to your description, I am quite sure whether the old user can connect server successfully.

Please confirm if only new users have the issues.

Does  the issue occur on OWA?  Did you have a migration on your environment?

I suggest you can do an Outlook connectivity test with https://testconnectivity.microsoft.com/   and see what went wrong.

I noticed that an error popped up after entering credentials, please post the error here for further analysis.

In addiction, please describe your exchange environment in detail.

Best Regards,

David