reverse is dns resolution on the ips isp hosting side.
your provider who own your ip address
assigns your domains mx record to your ip in a ptr text record on the dns server on there network. this allow you email to be verified and confirms you are a legitimate domain, not trying to hide or mask yourself.
your mx mail domain should always match your reverse ip resolution.

how to setup a domain on the a domain registrar -with out waiting for Dns Updates.
purchase domain at a domain registrar like cheap domains or godaddy
locate your ip address for your webserver in your welcome email
login to registrar add ips or edit host records
change ip address to your above ip for the following
-*
-www
-@
create a record for mail
create a txt record for spf entry
v=spf1 ip4:x.x.x.x/32 ~all"
creat mx record...

Here's an article that I recently wrote that
I'm sure you'll find helpful:

My Super-Effective Article Writing Formula
Copyright 2009 Willie Crawford

Here's the formula that I use to quickly write informative
articles that get results. For many of the articles that
I write my goal is to get visitors to a website where they
take some action related to the topic of the article.
Often the action that they take is to buy some product that...

There is a new service where you get paid
for pointing out your favorite videos from
sites like YouTube... or any site that allows
you to embed their code in your pages.


The way it works is that you sign up for
an account here:
http://GetPaidToShareVideos.com

In the back office of your account you
enter your Google AdSense ID. Then you
build as many pages on the site as you
want to. You build these pages by copying...

Sokule is a brand new social networking site, that feels a lot like Twitter except that it was designed for marketers, meaning it has built-in monetization.

You can plug your Clickbank ID into your profile, and have Clickbank ads show up on the page your followers/visitors see.

You can add up to 5 of your own links to the sidebar.

You can add up to 5 videos or pictures to the sidebar.

There are provisions for paid upgrades, and an affiliate program...