"Warning: could not message for past four hours" message

I get the following message back when sending mail to another .mac account, even though the message I sent has been delivered. A similar message also shows up in the mail program of Windows and Mac users when they try to send an email to my .mac account, always referencing "seller@gold-shopbizz.co.uk". Their email actually comes through to me, but they think it has not because they get this weird message saying that their email is not delivered. It's getting almost impossible to use my .mac account because of this problem. Is there any way to prevent this short of not using my .mac account?

Here's a copy of the error message.

Thanks!

jwulf



From: MAILER-DAEMON@mac.com
Subject: Warning: could not send message for past 4 hours
Date: September 19, 2007 10:05:52 PM EDT
To: slswulf@comcast.net

********************************************
** THIS IS A WARNING MESSAGE ONLY **
** YOU DO NOT NEED TO RESEND YOUR MESSAGE **
********************************************

The original message was received at Wed, 19 Sep 2007 14:18:17 -0700 (PDT)
from mail044-e1000g351000 [10.150.72.44]

----- Transcript of session follows -----
451 gold-shopbizz.co.uk: Name server timeout
Warning: message still undelivered after 4 hours
Will keep trying until message is 1 week old
Reporting-MTA: dns; smtpout.mac.com
Arrival-Date: Wed, 19 Sep 2007 14:18:17 -0700 (PDT)

Final-Recipient: RFC822; seller@gold-shopbizz.co.uk
Action: delayed
Status: 4.4.3
Last-Attempt-Date: Wed, 19 Sep 2007 19:05:52 -0700 (PDT)
Will-Retry-Until: Wed, 26 Sep 2007 14:18:17 -0700 (PDT)