ErrorConnectionFailed: We were unable to connect to the server.
Attempt to open your OWA URL from an external network from a system that is not joined to your domain. If OWA is loaded in a timely manner, check your server resources:
- Check server CPU usage.
- Check memory usage.
- Check disk I/O usage using performance monitor.
- Check for over-utilization of network.
The most common problem encountered is the over-utilization of network. This means that you are attempting to migrate too many mailboxes simultaneously, and do not have enough bandwidth to execute them. Refer to our article describing network utilization. Once you have a better understanding of network utilization, configure the correct number of mailboxes you can migrate simultaneously.