Host Unreachable for 1 domain

[Strongbow]

Messages sent by our users to one specific external domain are always failing, and end up sitting in the Exch 5.5 Outbount Messages Awaiting Delivery Queue, all with the status "Host Unreachable".

I have used nslookup on the server to make sure that the DNS is resolving the IP of the destination mail server correctly, which it appears it is, and no other domains seem to be effected.

Any ideas what could be causing this problem?

 

[Serbtastic]

Just because the IP address resolves correctly does not mean the remote host has an MTA listening at that IP.

Try telnetting to the remote mail server on port 25 and see if you get a response:

telnet <remote mail server IP> 25