Reverse DNS and RFC 2317

[Len Conrad]

>The main problem I have found is when remote servers use Reverese DNS
>lookups to varify your address

Look at the type of aggressive DNS validations, including reversing the 
SMTP client's ip, a first-class MTA will perform to try to prevent mail abuse:

http://postfix.eu.org/uce.html

More and more mail servers are performing these kinds of DNS validations, 
so the reverse delegation and PTR records of at least a mail server are 
increasingly important for reliable mail delivery.

Len