UPDATE
[2010-04-28 14:30:48 | Lars Rohrbach]
Normal IMAP service has been restored.
The problem appears to be storage-related. File system access issues (stale NFS file handles) led to
the imap server accepting incoming email but
not being able to deliver to people’s inboxes.
Before the message serving processes were stopped and
restarted and file systems remounted, there were over
3500 messages stuck in the queue for delivery to people’s inboxes.
No email was lost, and all queued email has now been delivered.
Resolved as of 2010-04-28 14:12:00