I am working on migrating an on premise Exchange 2010 server to Office365 Exchange Online.
I am doing a cutover migration as we have less than 100 mailboxes and the cutover is going to happen in a few days.
When I create the migration endpoint, it fails. I then went to https://testconnectivity.microsoft.com and ran the Microsoft Office Outlook Connectivity Tests by choosing Outlook Connectivity (Autodiscover is not setup for this server). The test shows that everything passes except the last part. The part that fails is "Testing the MAPI Mail Store endpoint on the Exchange server" but it doesn't give much information about why it failed.
I tried disabling and re-enabling Outlook Anywhere but it does not work.
I tried changing the authentication type from Basic to NTLM but that did not make it work.
I tried using Exchange Remote instead of Outlook Anywhere and that worked, but you cannot use Exchange Remote for a Cutover Migration. If you are going to do a Cutover Migration you must use Outlook Anywhere.
After some research I decided to go with the get rid of all of it and start over approach.
servermanagercmd -r rpc-over-http-proxy
servermanagercmd -i rpc-over-http-proxy
Then I logged into Office365 Exchange Admin and went through the migration wizard. Everything worked.
https://social.technet.microsoft.com/Forums/exchange/en-US/a8ce9a53-82e3-4709-b58c-231eb6d74aa2/testing-http-authentication-methods-for-url-httpsowamydomaincomrpcrpcproxydll-fails?forum=exchangesvr3rdpartyappslegacy