Outlook For Mac 15.12.3 stays connecting to my exchange server

Any chances the company could have made changes to the settings?
I would try removing then re-adding the account to trigger a new auto-discovery.
If that doesn't work, I would check whether Mail can connect to the same server, and if yes, through what address (again, I'm worried about redirections when you input the server address).
           Corentin

Do not believe so.  A colleague is able to use 15.12.3 but he is running El Capitan.

I reverted to 15.11.1, purchased Office365 for a month so I could activate it and I am able to connect to exchange again.  So something changed after 15.11.1 that causes this issue.  I had it with 15.11.2 as well.

I've noticed similar issues when my password keychain entries were having problems.

Launch the Keychain Access application found in Applications > Utilities. Choose Keychain Access menu > Keychain First Aid. Verify your keychain first. If you see problems then repair them.

You may find it helpful to search through your saved passwords for your Exchange server's name and delete your saved password for it. The next time you launch Outlook, you should receive a prompt to re-enter your password. This may get you connected again.

Hope this helps!

Try testing in a new Profile (Identity)

Create a new Profile. 

• To create a new profile, in Finder, browse to the Application folder. Press CTRL and then click Microsoft Outlook to see the contextual menu, and then click Show Package Contents.
  
• In the Contents > SharedSupport folder, double-click Outlook Profile Manager.
  
• In the Outlook Profile Manager window, click the Add Image button and give the profile a name.
  
• Next, click the Options button and click Set as Default.
  
• Open Outlook
  
  TIP: You might want to select Keep in Dock to make it easy to get back to the Profile Manager (previously called Database Utility)

Thanks for the reply.  I updated to 15.13.1 and it worked for a brief period.  I noticed that by default it was using my email address for user name instead of the username specified.  I replaced it with the correct username and it worked.  

But, i just restarted my computer and I am having the same issue.  I've deleted all passwords in my keychain with the name Exchange or anything resembling my companies address or webmail url but I am still getting the error.  Again, my login window brings up the incorrect username (it uses my email).

I tried to login with incorrect credentials and i get asked again to enter my credentials.  When I enter my correct credentials then it just hangs with "Connecting to: <Account Name>".

I notice that it tries to connect to several of my companies exchange servers so it's trying to connect.  Not sure why this is happening.

With the new version, i cannot login to the exchange server.  I copy and paste the URL for the Exchange server on my browser, the EWS/Exchange.asmx url, and type in my username and password and I am able to login.

I do see this a lot in my console.app

Reverted to 15.11.1 and was able to connect fine.  Created a new profile and was able to detect exchange settings and connect just fine.  For both 15.11.1 and 15.13.1, I used the same credentials.  Again one thing to note is that with 15.13.1 the username defaults to my email address instead of what I specify in the username field for my account.

No longer receiving the 

Microsoft Outlook[747]: Stream 0x7be94fe0 is sending an event before being opened

I have this problem as well on version 15.14.2 (150923). However I'm not able to revert back to 15.11.1, since I don't have installation media for this version.

Any suggestion is appreciated.