Whilst we believed we had resolved problems with web-11 yesterday, they seem to have re-appeared overnight.
Engineers are investigating and we hope to have the problem resolved shortly. In the mean time, to ensure no emails are lost, we are in the process of disabling the SMTP server on this machine as we work to identify and resolve the main problems with the server
UPDATE
Engineers restored service after clearing the broken email queues at 11am … we are continuing to monitor the server through the day and overnight in case the problem re-surfaces.
At this stage we believe the issue to have been caused by a number of rogue emails introduced into the queues through a compromised web hosting account. The compromised account has been suspended pending cleansing, and the corrupted messages removed from the email queues.