[via Bertrand, 1] SPF is an add-on to SMTP . To understand the difference to a blacklist take this example:
You ask SPF: \”I have someone coming from a certain IP address. They claim to be a certain sender. Are they for real?\” SPF will tell you one of four things:
1. The sender is good.
2. The sender is bad.
3. The sender may be good or bad.
4. SPF doesn\’t know.
SpamAssassin will use SPF in version 2.70.