Over one month ago I setup a new Server 2012 / Exchange 2016 with the intention of migrating the existing Exchange 2010. No disruption of services was the highest priority so installation progressed at a glacier rate. We finally reached a point where both mail server were operational, the 2016 server could send out email, the 2010 server continued to run the show. Last weekend I changed firewall settings so that the new 2016 server handled both inbound and outbound email and proxied down to the 2010. Worked great for about 5 days; no one was even aware of the change. As of last night...
1) 213 outbound emails stuck in queue
2) OWA gets a "page not found error"
3) Exchange Admin Center shows the login screen but displays a blank page and hangs. Even more interesting is the ECP folder is empty. There is only a config file.
Temporary fix - changed the firewall settings back to the old server. It would be nice to get the 2016 to deliver the emails stuck in the queue.
Short of completely reinstalling Exchange 2016, is there a way of fixing this? And more importantly, how did it happen?