Add SSL doc

README.md

@@ -540,6 +540,7 @@ You could make a donation to SimpleLogin on our Patreon page at https://www.patr
 The above self-hosting instructions correspond to a freshly Ubuntu server and doesn't cover all possible server configuration.
 Below are pointers to different topics:
 
+- [Enable SSL](docs/ssl.md)
 - [UFW - uncomplicated firewall](docs/ufw.md)
 - [SES - Amazon Simple Email Service](docs/ses.md)
 - [Upgrade existing SimpleLogin installation](docs/upgrade.md)

docs/ssl.md

@@ -0,0 +1,42 @@
+It's highly recommended to enable SSL/TLS on your server, both for the webapp and email server.
+
+This doc will use https://letsencrypt.org to get a free SSL certificate for app.mydomain.com that's used by both Postfix and Nginx. Letsencrypt provides Certbot, a tool to obtain and renew SSL certificates.
+
+To install Certbot, please follow instructions on https://certbot.eff.org
+
+As of today (March 25 2020), you can install Certbot by using these commands:
+
+```bash
+sudo apt-get update
+sudo apt-get install software-properties-common
+sudo add-apt-repository universe
+sudo add-apt-repository ppa:certbot/certbot
+sudo apt-get update
+sudo apt-get install certbot python-certbot-nginx
+``` 
+
+Then obtain a certificate for Nginx, use the following command. You'd need to provide an email so Letsencrypt can send you notifications when your domain is about to expire.
+
+```bash
+sudo certbot --nginx
+```
+
+After this step, you should see some Certbot lines in /etc/nginx/sites-enabled/simplelogin
+
+Now let's use the new certificate for our Postfix.
+
+Replace these lines in /etc/postfix/main.cf
+
+```
+smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
+smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
+```
+
+by 
+
+```
+smtpd_tls_cert_file = /etc/letsencrypt/live/app.mydomain.com/fullchain.pem
+smtpd_tls_key_file = /etc/letsencrypt/live/app.mydomain.com/privkey.pem
+``` 
+
+Make sure to replace app.mydomain.com by your domain.