Troubleshooting EWS connectivity (Office 365)

CodeTwo Office 365 Migration attempts to connect to EWS (Exchange Web Services) during the Configuration step of the source/target server connection wizard. If the connection cannot be established, you will get the following error message:

O365 Migration troubleshooting EWS connection
Fig. 1. Failure to connect to Exchange Web Services.

Once you click Details, you will get a more detailed description of the error. The solutions below should help you deal with the most common EWS connectivity issues.

The request failed. The remote server returned an error: (401) Unauthorized.

There are three known reasons why this error may occur:

  • the CodeTwo migration application registered with your Azure AD tenant is missing the full_access_as_app permission (find out how to assign it here),
  • the SMTP email address of the account used to register the application in Azure AD is different than its UPN (User Principal Name), 
  • the application has just been registered, but not all changes have been propagated in your Azure AD. Wait awhile and try configuring the connection again.
The SMTP address has no mailbox associated with it.

You will get this error if the email address provided in the Application details step of the server connection wizard is not mailbox-enabled (it is not assigned an Office 365 license). You will also get this message if the provided email address is from a different Office 365 tenant than the one determined by the Tenant ID.

AADSTS700016: Application with identifier '<Client ID>' was not found in the directory '<Tenant ID>'.

This error occurs if:

  • CodeTwo Office 365 Migration has been deleted from your Azure AD. If so, make sure to register it again (automatically or manually),
  • you have provided incorrect Client ID and/or Tenant ID in the Application details step of the server connection wizard. Make sure that you have provided correct registration details and try again.
  • the application has just been registered, but not all changes have been propagated in your Azure AD. Wait awhile and try configuring the connection again (in the server configuration wizard, click Back, then Next to return to the Configuration step and click Configure).

See also

How the Exchange throttling policy impacts the migration process

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