base: Don't install postfix on mail servers

roles/base/tasks/RedHat.yml

@@ -5,11 +5,15 @@
   with_items:
     - selinux        # selinux first to get fcontexts working
     - iptables
-    - postfix
     - rsyslog
   loop_control:
     loop_var: role
 
+- name: install postfix
+  include_role:
+    name: postfix
+  when: "'mail' not in {{ group_names }}"
+
 - name: install packages
   package:
     name: "{{ item }}"