I am trying to migrate 75 users mailboxes from Exchange2007 on premise to Office365. Their email accounts are setup in Office365 already. I have not however migrated any email from their on premise mailboxes to their cloud mailbox. I am trying to use Microsoft's Migration tool, but am failing the connectivity test with the following
Testing HTTP Authentication Methods for URL https://webmail.newbridge-college.ie/rpc/rpcproxy.dll?mail07.newbridge-college.ie:6002
The HTTP authentication test failed.
A Web exception occurred because an HTTP 404 - NotFound response was received from IIS6.
I have attached screenshot. OWA is working fine. Any ideas