SPF policy data is published on a DNS server in a TXT record. DNS resolvers typically cache SPF data to reduce lookup traffic. Sender domains do not have to run new servers to advertise SPF information; instead, SPF uses the connecting client's IP address and information from the SMTP envelope to evaluate the SPF policy document published via DNS. After the policy is evaluated, the message is classified and handled accordingly. For additional information about SPF, go to the SPF community at http://spf.pobox.com.
Example:
If a spammer forges mail from the mail server imaspammer.com and uses a different domain in the From address, such as john.doe@notaspammer.com, the receiving email server checks the SPF record for notaspammer.com. If it finds that john.doe@notaspammer.com is not listed as a legitimate email sender on notaspammer.com, the message fails and is processed by the SPF settings on the SPF Options page |
