Reverse DNS Lookup - Pass/Fail?

[royalmail]

This is in regard to mail servers rejecting mail from an incoming host after a reverse DNS check.

What are the requirements in order for an incoming host to pass the reverse DNS check?

If the reverse DNS lookup returns a DNS name, does this qualify as a pass?

Can the result be any old DNS name as long as an answer is received?

What happens if the reverse DNS lookup yeilds 2 or more results? Would that class as a fail?

 

[ChrisAC]

Most servers just make sure that a reverse record exists. Some do a double check so they look at the reverse record and they do a forward look up to make sure that the two match.

Chris.

**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[lhuegele]

A reverse lookup is when you take the name the server is saying it is, do a reverse lookup in DNS and see if the IP address in the public DNS records match the IP address that the said server is using to connect. If there is not a match, it fails. If it IS a match, the connection can proceed.

Your ISP should be able to set-up a reverse DNS record for your mail server.

Good luck.

 

[ChrisAC]

Not quite! The name that a server gives in its "helo" to the SMTP server doesn't have to match DNS at all. Most servers have a name that is different to the DNS name. Most reverse DNS implementations will simply check the IP address to see if it has ANY reverse DNS set up. If it does then some will do a forward lookup on that name to see if the IP resolves back to the connecting host. The name that the IP address resolves to doesn't have to match the name of the server.

Chris.




**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************