MRSPROXY.SVC’FAILED BECAUSE NO SERVICE WAS LISTENING ON THE SPECIFIED ENDPOINT. THE REMOTE SERVER RETURNED AN ERROR: (404) NOT FOUND
You get an error when you’re trying to setup Hybrid configuration between your Exchange On-premises and Exchange Online.
After I had one issue like this I did some research and used Fiddler/Wireshark to check for traffic I noticed that Exchange was not encrypting traffic and testing the Migration Server Availability was reporting that the MRS service was not listening on the supposed port which is 443.
In this case the solution was pretty easy, but still you’ll have to make a hard choice of choosing to place Exchange behind a load balancing with SSL Offloading on or not.
In my case I had to turn off the SSL Offloading on the Load balancer and that alone was enough to get this working.
Make sure that SSL Offloading is disabled on OWA/OA and Load balancer if there’s one.