roles/postfix: Deploy Postfix MTA

The *postfix* role installs and configures the Postfix MTA. It currently
supports a number of modes, including direct transfer and relay. Relay
mode supports STARTTLS security and PLAIN authentication.

roles/postfix/templates/sasl_passwd.j2

@@ -0,0 +1,5 @@
+{% if smtp.mode == 'relay' %}
+{% if smtp.auth|d('none') != 'none' and smtp.username is defined %}
+[{{ smtp.host }}]:{{ smtp.port|d(25) }}	{{ smtp.username }}:{{ smtp.password }}
+{% endif %}
+{% endif %}