[MrBen]

Hi John,

Ah that would probably explain it. There are lists of dynamic IP addresses such as the one at SORBS because they wouldn't typically be sending email directly out on to the Internet. Users should really be using their ISPs SMTP server (as can be seen in the Additional Information text at SORBS "Dynamic/Generic IP/rDNS address, use your ISPs mail server or get rDNS set to indicate static assignment."). I can only assume that the domain you are sending to has now decided to block email sent from dynamic IPs to try and reduce the number of spam + virus-infected emails received from infected computers. It is not an Exchange configuration problem.

It kind of defeats the object of running your own SMTP server, but as a work around I think you can configure Exchange to pass email on to ntl:'s SMTP server (from where it will be sent out onto the Internet). This should resolve your problem... but also puts you at the mercy of ntl:'s outgoing mail server! I can't remember off-hand how to configure it, but if you need assistance I can look it up on my SBS server tomorrow.

The other route is to maybe try and get the domain at the other end to whitelist your IP address (depends how well you know them though!) but I fear you may eventually run into another domain that also implements this type of email blocking.

Ben