Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

SPF validates the "MAIL FROM:" part of the SMTP protocol. Unlike Sender ID, it has nothing to do with the "From:" header of the mail message.

A compliant SMTP server is supposed to return bounces (not rejects) to the address given in "MAIL FROM:"; spammers don't want bounces, so they tend to use false addresses in "MAIL FROM:", while legitimate users do want bounces, so they use genuine addresses in "MAIL FROM:"