Networking / Beginners

---

Sender Policy Framework Overloading

Sender Policy Framework (SPF) is an example of a protocol that overloads existing DNS data types. SPF is an attempt to authenticate email and reduce undesirable email (spam). This protocol works by storing sender information in the TXT field. For example:

$ host -t txt abc.com
pobox.com descriptive text "v=spf1 mx mx:fallback-relay.%{d}
a:webmail.%{d} a:smtp.%{d} a:outgoing.smtp.%{d}
a:discard-reports.%{d} a:discards.%{d} mx:stor" "e.discard.%{d}
a:emerald.%{d} redirect=%{l1r+}._at_.%{o}._spf.%{d}"

The TXT field contains the SPF information. It specifies the authorized sources for email from the pobox.com domain.