SPF - Sender Policy Framework

SPAM generally contains a false sender address (return-path), this is "Sender Address Forgery". This is a problem if the email address(es) that are forged in torrents of SPAM belong to you. You will know this is the case when you receive the bounces and out-of-office replies from those SPAM emails.

SPF or Sender Policy Framework allows you to protect your domain from this abuse.

SPF is a record in the Domains DNS zone that allows an email recipient to verify that email originated with the server(s) designated by the domain owner.

The SPF Project home page is the place to start, read up:

The record itself is fairly complex but there are tools to both make:

And to verify them:

After my email received long term Sender Address Forgery I finally dove in and realized how simple SPF is to implement and plan to make it a default on client domains as well.

Get in there and FIGHT the SPAM!