Created SSL (markdown)

docs/content/ssl.md

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+# docker-mailserver with ssl
+
+There are multiple options to enable SSL:
+
+* using [letsencrypt](https://letsencrypt.org/) (recommended)
+* using self-signed certificates with the provided tool
+
+After installation, you can test your setup with [checktls.com](https://www.checktls.com/TestReceiver).
+
+## let's encrypt (recommended)
+
+To enable Let's Encrypt on your mail server, you have to:
+
+* get your certificate using [letsencrypt client](https://github.com/letsencrypt/letsencrypt)
+* add an environment variable `DMS_SSL` with value `letsencrypt` (see `docker-compose.yml.dist`)
+* mount your whole `letsencrypt` folder to `/etc/letsencrypt`
+* the certs folder name located in `letsencrypt/live/` must be the `fqdn` of your container responding to the `hostname` command.
+
+You don't have anything else to do. Enjoy.
+
+## self signed certificates
+
+You can easily generate a self-signed SSL certificate by using the following command:
+
+    docker run -ti --rm -v "$(pwd)"/postfix/ssl:/ssl -h mail.my-domain.com -t tvial/docker-mailserver generate-ssl-certificate
+
+    # Press enter
+    # Enter a password when needed
+    # Fill information like Country, Organisation name
+    # Fill "my-domain.com" as FQDN for CA, and "mail.my-domain.com" for the certificate.
+    # They HAVE to be different, otherwise you'll get a `TXT_DB error number 2`
+    # Don't fill extras
+    # Enter same password when needed
+    # Sign the certificate? [y/n]:y
+    # 1 out of 1 certificate requests certified, commit? [y/n]y
+
+    # will generate:
+    # postfix/ssl/mail.my-domain.com-key.pem (used in postfix)
+    # postfix/ssl/mail.my-domain.com-req.pem (only used to generate other files)
+    # postfix/ssl/mail.my-domain.com-cert.pem (used in postfix)
+    # postfix/ssl/mail.my-domain.com-combined.pem (used in courier)
+    # postfix/ssl/demoCA/cacert.pem (certificate authority)
+
+Note that the certificate will be generate for the container `fqdn`, that is passed as `-h` argument.
+Check the following page for more information regarding [postfix and SSL/TLS configuration](http://www.mad-hacking.net/documentation/linux/applications/mail/using-ssl-tls-postfix-courier.xml).
+
+To use the certificate:
+
+* add an `DMS_SSL=self-signed` to your container environment variables
+* if a matching certificate (files listed above) is found in `postfix/ssl`, it will be automatically setup in postfix and courier-imap-ssl. You just have to place them in `postfix/ssl` folder.
+
+### Testing certificate
+
+From your host:
+
+    docker exec mail openssl s_client -connect 0.0.0.0:25 -starttls smtp -CApath /etc/ssl/certs/
+
+or
+
+    docker exec mail openssl s_client -connect 0.0.0.0:143 -starttls imap -CApath /etc/ssl/certs/
+
+
+And you should see the certificate chain, the server certificate and:
+
+    Verify return code: 0 (ok)