Just a few hours ago, we can no longer send mail to our client. Each email sent to them bouncesback with the following....
Your message did not reach some or all of the intended recipients.
Sent: 27/04/2009 20:40
The following recipient(s) could not be reached:
firstname.lastname@example.org on 27/04/2009 20:40
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
< mk-filter-7.mail.uk.tiscali.com #5.0.0 smtp; 5.1.0 - Unknown address error 550-'Mailbox is inactive' (delivery attempts: 0)>
All mailboxes on the exchange server are fine, and we can see no problem.
The server is Exchange Server 2003 SP2