Unknown address error 550 - Mailbox is inactive (delivery attempts: 0)


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.

      Subject:      test
      Sent:      27/04/2009 20:40

The following recipient(s) could not be reached:

      administrator@xxx.co.uk 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

Who is Participating?
tekniteAuthor Commented:
It looks like it was an ISP issue at their end. Thanks for you help and guidance.
Hypercat (Deb)Commented:
The error message indicates a bad recipient address.  Assuming these are external emails, it has nothing to do with your internal email server. So unless you are responsible for managing your client's email system, I would just have someone give them a call and let them know that you are having trouble sending them email.  Since it's happening with all addresses for that client, it's apparently some sort of systemic problem, not just a bad email address for a particular recipient.
tekniteAuthor Commented:
Thanks, we are responsible for the server. Our initial emails were to 2 of the partners of the firm, and as for testing we used the administrator account, all bouncing back.
This customer is on an SMTP feed and the MX record is pointing as it should in the right place.

Any suggestions?
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Hypercat (Deb)Commented:
Have you checked to be sure that their domain name registration is not expired?  I've had this happen a couple of times over the years, and even once in the past couple of months, to several of my clients who are responsible for their own domain name registration renewal.  They just ignore the emails, not understanding what they are for, and then all of a sudden nothing works...
tekniteAuthor Commented:
Yes i agree with you, its the part the client never understands and then wonders whats wrong!
It only expires in Feb 2010
Hypercat (Deb)Commented:
HMMM, ok, so that's not it - I guess that was tooooo easy, right? Do you have SMTP logging turned on at your site and/or the client site?  If not turned on already, turn it on and re-test.  Then you can check the logs and see what if any communication is actually happening between the two servers.  Are they not getting any emails, or just not getting emails from you?
Also, have you checked their domain through www.dnsstuff.com or another on-line DNS service? Can you successfully do an nslookup on their domain and MX records?
Is this an SBS server or standard Exchange/Windows?  Is it Exchange 2003 with Windows 2003, or some other version(s)?
tekniteAuthor Commented:
I'm not sure on the logging side. I'll do a check.
Its Windows 03 R2 Std and Exch 03 SP2 STandard
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