Sender Policy Framework is basically used to over come spoofing of the emails. E-mail spoofing is a term used to describe fraudulent e-mail activity in which the sender address and other parts of the e-mail header are altered to appear as though the e-mail originated from a different source
Adding SPF record in the DNS will help to define from which IP address outgoing mail will be sent for the particular domain. Any receiving domain will check all the receiving mails if it’s coming from the valid registered sender IP address. If sender IP address is not registered or if spoofed by different machine then mail can be directly blocked as spam.
For more information www.openspf.org