libspf2 implements the Sender Policy Framework, a part of the SPF/SRS
protocol pair. libspf2 is a library which allows email systems such
as Sendmail, Postfix, Exim, Zmailer and MS Exchange to check SPF
records and make sure that the email is authorized by the domain name
that it is coming from. This prevents email forgery, commonly used by
spammers, scammers and email viruses/worms.