Merge pull request ajgon#10 from phunehehe/installation-instructions

Installation instructions

Author: ajgon

INSTALL

@@ -0,0 +1,45 @@
+ 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. Place `gpg-mailgate.py` in `/usr/local/bin/`
+ 4. Place the GnuPG directory in `/usr/lib/python2.7/` (replace 2.7 with your
+    Python version)
+ 5. 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
+
+ 6. Add the following to `/etc/postfix/main.cf`
+
+        content_filter = gpg-mailgate
+
+ 7. Restart postfix.
+
+
+## Note 1
+
+It is possible to create a dedicated user to store the PGP public keys with
+these example commands:
+
+    useradd -s /bin/false -d /var/gpg -M gpgmap
+    mkdir -p /var/gpg/.gnupg
+    chown -R gpgmap /var/gpg
+    chmod 700 /var/gpg/.gnupg
+    sudo -u gpgmap /usr/bin/gpg --import /home/youruser/public.key --homedir=/var/gpg/.gnupg
+
+  - Replace `/home/youruser/public.key` with the location of your public key
+  - `/home/youruser/public.key` can be deleted after importation
+  - Confirm that it's working: `sudo -u gpgmap /usr/bin/gpg --list-keys --homedir=/var/gpg/.gnupg`
+  - Use `keyhome = /var/gpg/.gnupg` in `gpg-mailgate.conf`