1. Ensure that GPG is installed and configured. Also make sure public keys for all of your potential recipients are available in the GPG home directory used for `keyhome` in step 2. 2. Configure `/etc/gpg-mailgate.conf` based on the provided `gpg-mailgate.conf.sample` 3. install some python dependencies `apt-get install python-m2crypto python-markdown python-requests` 4. Place `gpg-mailgate.py` and `register-handler.py` in `/usr/local/bin/` 5. Place the GnuPG directory in `/usr/local/lib/python2.7/dist-packages` (replace 2.7 with your Python version) 6. Add the following to the end of `/etc/postfix/master.cf` gpg-mailgate unix - n n - - pipe flags= user=nobody argv=/usr/local/bin/gpg-mailgate.py ${recipient} 127.0.0.1:10028 inet n - n - 10 smtpd -o content_filter= -o receive_override_options=no_unknown_recipient_checks,no_header_body_checks -o smtpd_helo_restrictions= -o smtpd_client_restrictions= -o smtpd_sender_restrictions= -o smtpd_recipient_restrictions=permit_mynetworks,reject -o mynetworks=127.0.0.0/8 -o smtpd_authorized_xforward_hosts=127.0.0.0/8 7. Add the following to `/etc/postfix/main.cf` content_filter = gpg-mailgate 8. Add `register: |/usr/local/bin/register_handler.py` to `/etc/aliases` 9. Restart postfix. 10. create a dedicated user to store the public keys with these example commands: usermod -d /var/gpg nobody mkdir -p /var/gpg/.gnupg mkdir -p /var/smime/certs mkdir -p /var/smime/templates chown -R nobody /var/gpg chown -R nobody /var/smime chmod 700 /var/gpg/.gnupg sudo -u nobody /usr/bin/gpg --import /some/public.key --homedir=/var/gpg/.gnupg - Replace `/some/public.key` with the location of a public key - `/some/public.key` can be deleted after importation - Confirm that it's working: `sudo -u nobody /usr/bin/gpg --list-keys --homedir=/var/gpg/.gnupg`