[taxcontrol]

It is these reverse lookups that are overloading the ISPs. I properly constructed business would, like you said, have their own DNS server to do a local lookup against.

However, what about the ISP's email servers? Add to that the load from business that are too small to have their own mail servers or DNS servers and you can see that there can be a significant load on the DNS servers.

Ideally, you would have an email filtering bastion host (email relay server) that would locally store the current DNS table. That way it could locally check the emails for a valid dns name prior to passing on to the internal email server. It could also do the scanning for viruses as well as blacklisted domains, pre and post tagging, etc.

[general_re]

Ideally, you would have an email filtering bastion host (email relay server) that would locally store the current DNS table. That way it could locally check the emails for a valid dns name prior to passing on to the internal email server.

And what happens in the case of new domains that have been legitimately registered, or old domains that have expired out of your local DNS cache? Your DNS box then has to go outside the LAN to do a lookup itself, and you're right back to square one.