We have rectified an issue with both the primary and backup mail servers.
Microsoft updates were applied to both of these machines earl;y this morning which required a reboot. When the servers rebooted, the SmarterMail service failed to restart as it was conflicting with another service on the box. Our monitoring service immediately picked this up and escalated the issue.
As this was the first time these boxes had been rebooted since mid-March, the problem was not discovered/rectified earlier.
We have now taken steps to ensure that both servers respond correctly after a reboot and would like to apologise for an inconvenience caused.