About Sender Policy Framework (SPF) Records

Sender Policy Framework (SPF) is an extension to the Simple Mail Transfer Protocol (SMTP). SPF allows software to identify and reject forged addresses in the SMTP MAIL FROM (Return-Path), a typical nuisance in e-mail spam.

Normal SMTP allows any computer to send an e-mail claiming to be from anyone. Thus, it's easy for spammers to send e-mail from forged addresses. This makes it difficult to trace back to where the spam truly comes from, and easy for spammers to hide their true identity in order to avoid responsibility.

SPF allows the owner of an Internet domain to use special format of DNS TXT records to specify which machines are authorized to transmit e-mail for that domain. For example, the owner of the example.org domain can designate which machines are authorized to send e-mail whose sender e-mail address ends with "@example.org". Receivers checking SPF can reject messages from unauthorized machines before receiving the body of the message.

As an example, NeatWorx publish an SPF record that looks like the following instructing a receiving domain about the list of servers that can send e-mail on our behalf and warning the recipient that originators other from this address are likely to be spam.  It is up to the receipient how they choose to deal with these records, but spam filtering system increasingly filter messages based on SPF pass or fail indicators in SPF headers.

neatworx.com IN TXT SPF v=spf1 mx ip4:72.55.156.169/27 ip4:xx.xx.xx.xx include:sympatico.ca –all

You don't actually need to understand all this, but the point is that we can adjust your SPF record for your domain to allow your sending SMTP server if SPAM rejection becomes an issue.

A good explanation of defining SPF records appears here - http://www.zytrax.com/books/dns/ch9/spf.html