SPF allows the owner of an Internet domain to use special DNS records to specify which machines are authorised to transmit e-mail for that domain. For example, the owner of the example.com domain can designate which machines are authorised to send e-mail whose e-mail address in the Return-Path ends with “@example.com”. Receivers checking SPF can then reject any e-mail that claims to come from that domain, but fails in a check against the IPs listed in the sender policy of this domain.