chore: Postfix should integrate Dovecot at runtime (#3681)

* chore: Better establish startup scope

* chore: Configure `main.cf` for Dovecot at runtime

target/scripts/helpers/aliases.sh

@@ -23,6 +23,7 @@ function _handle_postfix_virtual_config() {
   fi
 }
 
+# TODO: Investigate why this file is always created, nothing seems to append only the cp below?
 function _handle_postfix_regexp_config() {
   : >/etc/postfix/regexp