I have what I suspect is a DNS problem.
This is the situation. We have an Exchange server we host in-house. Some external mail service providers are unable to get to our mail server, the biggest problem is Comcast. I have a test machine on a Comcast network and I cannot ping the mail server by "ping mail.ourdomain.com", it comes back with Host Not Found. However, I CAN to a reverse lookup using "ping -a mail.ourdomain.com" and it returns the correct IP. I suspect that some top level DNS servers are not propagated from the provider that hosts or A and MX records, but that provider states that it's not their problem.
When I perform a nslookup from the Comcast test box and from another Internet Service Provider (Level3) with set q=mx then supply the mail.ourdomain.com, it returns a can't find, then "non-existent domain"
Any ideas on how to figure this out?