The pophash system solves a real problem for mail server with "moving" users. If you enable relay control, then only users originating from specific networks may use the SMTP server. With this strategy, any user who have successfully connect with the vpop3d server will be allowed in. The popauther.pl script maintain in real time the /etc/mail/pophash database and sendmail uses this db to grant relay or not (plus all the other databases it already uses).
vpop3d has been modified so it provides suitable information through the syslog facility.