Cannot create Exchange Online Migration Endpoint with Exchange 2007 Server using only NTLM Authentication

I've been battling an issue for a few days now and finally stumbled upon a workable solution via PowerShell.

Scenario

Client has an existing Exchange 2007 deployment.  The OWA instance is configured to only use NTLM authentication.  ExRCA (http://www.testexchangeconnectivity.com) comes back clean, and I can proxy log in to any mailbox on the server.

When configuring the migration endpoint through the EAC, I would receive an error that the migration endpoint could not be discovered, even after entering the credentials, server, and RPC proxy server values manually.

Solution

The solution ended up with my old friend PowerShell.  You can create migration endpoints through it using the New-MigrationEndpoint cmdlet.  The key was forcing the authentication to NTLM.

New-MigrationEndpoint -ExchangeOutlookAnywhere -Name NewEndPointName -ExchangeServer EXCHSERVER.DOMAIN.local -RpcProxyServer OWA.DOMAIN.com -Credentials (get-credential onpremiseaccount@domain.com) -EmailAddress onpremiseaccount@domain.com -SkipVerification -Authentication NTLM