Последовательность действий для установки POP Before SMTP на popa3d + Postfix 

1: cd /usr/ports/mail/popa3d
2: make
3: cd work/popa3d-popa3d-1.0
4: cp ../../files/pop-before-sendmail.patch pop-before-sendmail.patch
5: patch < pop-before-sendmail.patch
правим если нужно params.h
6: make
7: cd ../../
8: make install && make clean
9: cd /etc/mail/ && touch popauth && postmap popauth

Правим main.cf:
10: mynetworks = hash:/etc/mail/popauth
11: postfix reload

Правим inetd.conf
12: pop3    stream  tcp     nowait/10/5/2  root    /usr/local/libexec/popa3d   popa3d

перезапускаем inetd.