Incorrect Admin Credentials
The most common reason for a 401 is the admin username and/or password.
The admin username can be entered in any one of the following formats, however, some Exchange servers only allow one:
Username: IE firstname.lastname@example.org
Email Address: email@example.com
As for the password, the password will either be correct, incorrect or expired. If it’s expired it needs to be reset before it will be accepted.
The admin credentials can be checked by browsing to the EWS in a web browser and logging in. If they are correct you will be presented with an XML screen.
Incorrect Direct Exchange EWS URL
The correct method to find the Direct Exchange EWS URL is via Powershell. See our KB article: Determine the correct EWS URL for a migration
Incorrect Authentication Method
If your 401 error relates to the Auth Method, it will tell you so and it will advise which method to configure.
With legacy Exchange servers, ‘Basic’ authentication is not enabled by default so it will need to be changed to either NTLM or Negotiate (NTLM most of the time).
Office 365, on the other hand, will always be ‘Basic’.