Due to the fact that a significant majority of SPAM comes from forged addresses, a new Sender Policy Framework (SPF) standard is being implemented by a number of ISPs and mail hosts, including several major providers (Hotmail, Yahoo, AOL, etc). Those providers have begun to require SPF to allow mail through their networks. Mail systems will need SPF records for their domains if they want their mail to be accepted by those providers.

WHAT IS SPF?

SPF is an open standard created to stop forgery of FROM addresses. SPF helps mail servers distinguish forgeries from real mail by making it possible for a domain owner to say, "I only send mail from these machines."