Log message:
Spfmilter implements the Sender Policy Framework (SPF) as a milter, using 
either the libspf or libspf2 libraries. 

The idea of SPF is to prevent email forgery. Each participating site sets up 
a little definition of which hosts are allowed to send mail claiming to be 
from that site. When another site receives mail, it checks the 
permitted-senders definition for the originating site. If the check fails, 
the mail is rejected.