Установка stunnel:

   cd /usr/ports/security/stunnel
   make && make install (!) не торопимся делать clean
   Копируем из папки work в /usr/local/etc/stunnel - stunnel.cnf, затем делаем make clean.

Создаем сертификат:
   cd /usr/local/etc/stunnel && openssl req -new -x509 -days 365 \
      -nodes -config stunnel.cnf -out stunnel.pem -keyout stunnel.pem
   chmod 600 stunnel.pem && chown root:wheel stunnel.pem

Конфиг для stunnel:

   cert = /usr/local/etc/stunnel/stunnel.pem
   RNDfile = /usr/local/etc/stunnel/stunnel.rnd
   chroot = /usr/local/var/stunnel/
   setuid = stunnel
   setgid = stunnel
   pid = /run/stunnel.pid
   output = /var/log/stunnel.log
   ciphers = HIGH
   debug = 6
   compression = rle
   [pop3s]
   accept  = 995
   connect = 127.0.0.1:110

Делаем chroot:

   cd /usr/local/var && mkdir stunnel && cd stunnel
   mkdir etc && touch hosts.allow
   cd .. && mkdir run

Содержание hosts.allow:

   pop3s : ALL : allow
   ALL : ALL : deny

Права на директории /usr/local/var/stunnel

   drwxr-xr-x  2 root     wheel    512 Jul 30 20:31 etc
   drwxr-xr-x  2 stunnel  stunnel  512 Aug  3 15:55 run

Правим rc.conf, если у Вас запускается только popa3d из inetd:

   inetd_flags="-wWa 127.0.0.1"
   /usr/local/etc/rc.d/stunnel.sh start

Просмотр ciphers:

   openssl ciphers -v 'HIGH'