feat: add OS switch to install Postfix on Ubuntu instead of Exim MTA

tasks/configure_mail.yml

+---
+- name: Install and configure Exim MTA.
+  ansible.builtin.import_tasks: "mail/configure_exim.yml"
+  when: ansible_distribution == "Debian"
+  tags: [exim, mail]
+
+- name: Install and configure Postfix MTA.
+  ansible.builtin.import_tasks: "mail/configure_postfix.yml"
+  when: (( ansible_os_family == "RedHat" ) or (
+         ( ansible_distribution == "Ubuntu" ))
+  tags: [postfix, mail]
+

tasks/configure_exim.yml → tasks/mail/configure_exim.yml

 ---
-- name: Configure exim4
+- name: Install Exim4 MTA.
+  ansible.builtin.package:
+    name: "exim4"
+    state: latest
+
+- name: Configure Exim4.
   ansible.builtin.template:
     src: 'update-exim4.conf.conf'
     dest: "/etc/exim4/update-exim4.conf.conf"

tasks/configure_postfix.yml → tasks/mail/configure_postfix.yml

 ---
-- name: configure Postfix
+- name: Install Postfix MTA.
+  ansible.builtin.package:
+    name: "postfix"
+    state: latest
+
+- name: Configure Postfix MTA.
   ansible.builtin.blockinfile:
     path: "/etc/postfix/main.cf"
     owner: "root"

tasks/main.yml

@@ -118,15 +118,9 @@
   ansible.builtin.import_tasks: "configure_sar.yml"
   tags: [sar, sysstat]
 
-- name: Exim konfigurieren
-  ansible.builtin.import_tasks: "configure_exim.yml"
-  when: ansible_os_family == "Debian"
-  tags: [exim, mail]
-
-- name: Postfix konfigurieren
-  ansible.builtin.import_tasks: "configure_postfix.yml"
-  when: ansible_os_family == "RedHat"
-  tags: [postfix, mail]
+- name: Configure Mail Transfer Agent (MTA)
+  ansible.builtin.import_tasks: "configure_mail.yml"
+  tags: [exim, postfix, mail, mta]
 
 # - name: Glances-Server abschalten
 #   ansible.builtin.import_tasks: "configure_glances.yml"