[CentOS] postfix tightening

[ryanag at zoominternet.net]

On Fri, 2005-04-01 at 21:04 -0600, Mark A. Lewis wrote:
> 
> Riight. Ever done a reverse lookup on a RR IP? Rogers? SBC? All of
> them
> will have valid reverse entries.
See below.

http://searchcio.techtarget.com/sDefinition/0,,sid19_gci917504,00.html

"Reverse DNS (rDNS) is a method of resolving an IP address into a domain
name, just as the domain name system (DNS) resolves domain names into
associated IP addresses. One of the applications of reverse DNS is as a
spam filter. Here's how it works: Typically, a spammer uses an invalid
IP address, one that doesn't match the domain name. A reverse DNS lookup
program inputs IP addresses of incoming messages to a DNS database. If
no valid name is found to match the IP address, the server blocks that
message."