Steps for running qmail-masq:

1) install and configure qmail (if you're italian read my "Italian qmail HOWTO")

2) install qmail-qfilter and modify /var/qmail/bin/qmail-queue as shown above

  #!/bin/sh
  exec /var/qmail/bin/qmail-qfilter /usr/bin/qmail-masq.pl

4) copy the qmail-masq.pl to /var/qmail/bin and modify the permission

  # cp qmail-masq.pl /var/qmail/bin/
  # chown root:root /var/qmail/bin/qmail-masq.pl
  # chmod 755 /var/qmail/bin/qmail-masq.pl

3) copy qmail-masq.conf.example to /etc/qmail-masq.conf and modify it for your
needs (follow the instructions in the file)

   # cp qmail-masq.conf.example /etc/qmail-masq.conf
   # chmod 644 /etc/qmail-masq.conf
   # vi /etc/qmail-masq.conf

4) all is done, you don't have to restart qmail, try it sending some email and
enjoy it!