At 16:08 BST we were alerted by our monitoring system that mails were being queued that were destined for this Zimbra mailbox server.  Mailboxes that are hosted on this server will have been affected and their emails queued.  A restart of Zimbra on this mailbox server was required to restore service.  There was a brief outage for users of this mailbox server whilst the restart was performed.  Queued mail is currently being delivered.

We believe the problem is the same one which occurred on the 5th July.  We've been able to track the problem down and will be working with Zimbra to fix.

Please accept our apologies for the inconvenience caused.