I have heard that most spam filters use a reverse DNS lookup on the originating IP address of the sending SMTP server (or something like that) as part of the verification process. I want to make sure my emails will pass this check. How exactly can I verify that my emails are OK?
In researching it, I've noticed that if I look at the header of a valid email message coming from Gmail, I will see something like this:
Received: from mail-pz0-f185.google.com (mail-pz0-f185.google.com [18.104.22.168]) by mx.google.com with ESMTP id 10si2346996pxi.164.2009.07.22.22.26.19; Wed, 22 Jul 2009 22:26:19 -0700 (PDT)
When I do an nslookup on 22.214.171.124, it responds with mail-pz0-f185.google.com, which is what I would expect. If it responded with a different domain, then I assume that would indicate a problem and it would fail the check.
Is this what the reverse DNS lookup is all about or am I barking up the wrong tree?