We have an Exchange 2013 VM in Hyper-V running CU3. We took a checkpoint and attempted to install CU9, which failed. We then applied the previous checkpoint, expecting everything to go back as was; however no email can be sent or received. Users can connect to mailboxes, but if mail is sent it shows in Sent Items but is not sent (if sent from Outlook) or sticks in Drafts (if sent from OWA).
If we telnet to the server's external address on port 25 the connection is made but there is no response from the server; it's the same when connecting from another machine on the internal network (e.g. the DC). Connecting from the server itself locally by telnet gives the correct, expected response.
We have uninstalled the F-Secure for Exchange AV, and disabled the Malware Agent filter, and also disabled the Windows Firewall - but there's no change to the problem. We also deleted and recreated the Default Frontend receive connector, also with no change.
Nothing shows in the mail queue. Test-SMTPConnectivity reports "success" for all connectors. Test-Mailflow reports *FAILURE*.
How can we restore normal mail flow? Thanks in advance for any assistance.