http://www.emailarms.com This video explains everything there is to know about SPF (Sender Policy Framework) and how it's used to combat spam and forgery of your "From:" address.
Create An Spf Txt Record throughout Spf Record Example
Mailchannels: Spf Records - Applied Innovations inside Spf Record Example
Create A Spf Record On Godaddy - Mail-Tester intended for Spf Record Example
Creating An Spf Or Caller Id Record throughout Spf Record Example
Email Authentication Tool Cpanel Spf Record | Liquidlayer regarding Spf Record Example
Create A Spf Record On Gandi - Mail-Tester inside Spf Record Example