Sender Policy Framework (SPF) library and client in C.
SPF is a standard under development for email envelope sender
verification. Domain owners can specify who is qualified to send
mail for the domain by publishing SPF TXT records in DNS.
Read all about SPF at http://spf.pobox.com/

Author: James Couzens <jcouzens@6o4.ca>
WWW: http://www.libspf.org/