TCP DNS issue with Windows 2000 IIS5

[bluebird2000]

I am attempting to get to the bottom of a name resolution problem with IIS5.

The server was configured with two DNS entries, 213.120.62.97 and 213.120.62.98. I was alerted that this server was failing to process outbound email and noted an Event ID 4000 in the event log. (Reference the MS knowledgebase articles Q292278 and Q263237).

I have determined that there is a problem accessing port 53 TCP on these servers (managed by our ISP - BT Openworld).

I have checked the port filtering settings on this server, also the firewall settings and logs and can see the TCP SYN packets both on the local subnet, and passing through the firewall. I cannot see any packets in reply from the destination server (SYN-ACK or RST).

The ISP insist that they have not blocked port 53 TCP on their servers, and that the problem is at our mailserver.

I have resolved this problem by adding further DNS entries (which do allow a TCP connection).

Can anyone suggest a way of determining which router is dropping these packets? Has anyone else had this problem?

Any suggestions appreciated

 

[DG659]

BT Block SMTP relay unless you inform them that your running a mail server cant quite remeber the correct URL but try

http://www.btopenworld.com/helpbb

or just btconnect.com and browse about