With Exchange 2016 Hybrid setup, you might encounter an error while doing remote move migration. After selecting mailbox to move, the wizard gives you an error, that the "Endpoint MRSProxy" connection cannot be completed. After running command Test-MigrationServerAvailability -ExchangeRemoteMove -RemoteServer "ExternalUrl" You receive the following error. You can also find the same error from the IIS log. The problem you are facing, is related to the authentication method of EWS. To fix the problem, head to ECP - > Servers -> Virtual Directories -> EWS -> Authentication and add the Basic authentication.   Then when you run the command again, you will see it success. After this, you will be able to add new Remote Migration Endpoint.

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