SPF (define), Sender ID, and DomainKeys are relatively new technologies on the cutting edge of the fight against spam and false positives. The goal of all these technologies is to verify a message's sender is who he says he is. Falsifying sender addresses is a common practice among spammers.

The logic: if you make it harder for spammers to hide their identities, it's easier to hold them accountable for the e-mail they send. This may discourage their efforts. Though these technologies aren't silver bullets for stopping spam, they should help diminish false positives. They're the first steps toward a technical solution to spam, combined with reputation, authentication, and accreditation technologies.

The three technologies are somewhat hierarchical. SPF provides the most basic level of authentication. Sender ID takes it a step further, while DomainKeys offers an additional verification level. SPF is already used, most notably by America Online, to filter spam.

Read all about SPF in ClickZ' "An E-Mail Marketer's Guide to Deliverability"
Read all about Sender ID in ClickZ' "An E-Mail Marketer's Guide to Deliverability"

Source: ClickZ