No Transport Provider

My client's email was working fine until the end of last week. Basically they have a small workgroup of four PC's that all use Outlook (2K and XP) to send/receive email over the ADSL connection. They use their own domain name and have paid to have this domain added to the SMTP gateway of their service provider (
All was fine until they decided to cancel a hosting account in error that was hosting their domain. With out going into too much detail, the domain is now active again and POP3 is working fine. The only things changed were the name servers the domain was using. The domain name is exactly the same.
Since this has happened the BT SMTP gateway is bouncing email back to the sender with the "No Transport Provider" . I've contacted BT and have been told that the domain name is definately listed on the SMTP gateway, and that I should change the Outlook setting to "My outgoing server requires auth...." with the correct log in details. I've tried this (and it's something that was not needed before this happened) but to no avail. BT won't support anything other than OE, but I'm sure it's not a client problem, rather a server problem.
Any ideas?
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That error is sually an addressing format error on the sender side, but it sounds like the scope is bigger than just that.

So..... BTCONNECT has allowed <> to send SMTP via BTCONNECT's servers, correct? Thus their OE clients point SMTP and POP3 to MAIL.BTCONNECT.COM (or similar)? Inbound works and outbound doesn't?

Perhaps the account they canclled had been handling their e-mail relaying and the new setup doesn't handle it identcally, check out for possible solutions (although it doesn;t quite sound like your clients situation).

Strange that th eonly change was the name server, I would expect this if the mail relay server config changed.

Also see this post, at the bottom a user said it was spyare...again this doesn't sound like the fix for you but at least it's more info.
Check the DNS entries on your server to see if the new name servers are entered exactly as it is supposed to.

In exchange SMTP Protocols > SMTP Properties > Delivery Tab > Advanced button > Configure button > enter the ip's of the correct nameservers. It may still be referring the removed records.

cyansolAuthor Commented:
Guys, thanks for your comments. Problem has now been solved. BT were at fault. Their SMTP gateway has been causing problems for some clients using They have now asked me to use and authenticate the outgoing server in Outlook. Email is now flowing. I'll split the points with you both for answering so promptly. Thanks again.
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