Quote Originally Posted by DazzyD View Post
Paul, from the error message you pasted in, I'd say this was an issue with Talk Talk's mail system as the incoming mail server rather than your own outgoing mail server. The error gives the incoming mail server details, after all. Have you had any issues sending mail to anyone else? If your own host is blocking your emails then none would go out. If it's only Talk Talk customers you can't email then it's their blacklist, or one of the Spamhaus lists that they make their decisions from, that is causing the problem.
I'm sure it's a Talk Talk problem as everything else is sending fine. I've spoken to the client now so all is good.