Introduce postfiy_type to differ between configuration types

README.md

@@ -8,9 +8,20 @@ Use this role to setup a Postfix mail server. It comes with the following additi
 - optional: [OnionMX](https://github.com/ehloonion/onionmx)
 - optional: Unbound
 
+## General type of mail server configuration
+
+You can select via the variable `postfix_type` a pre-defined set of configuraion options that best meets your needs.
+- `internet`: Mail is send received directly using SMTP. TLS is enabled.
+- `internal`: Mail is sent to another machine on the same network for delivery. TLS is disabled. Only listens on port 25.
 
 ## Variables
 
+### Required
+
+| Variable | Value | Default | Note |
+|--|--|--|--|
+| `postfix_type` | str | `internet` | Determines how to setup Postfix. Choose `internet` or `internal` |
+
 ### Scope: misc
 
 | Variable | Value | Default | Note |