use become

handlers/main.yml

@@ -1,5 +1,5 @@
 ---
-- name: Restart postfix
+- name: Restart service
   service:
     name: postfix
     state: restarted

tasks/config.yml

@@ -1,4 +1,6 @@
 ---
+- name: Setup postfix
+  block:
   - name: Configure postfix
     template:
       src: etc/postfix/main.cf.j2
@@ -55,3 +57,4 @@
     when: not senderdb.stat.exists or sender_result.changed
     register: senderdb_update
     notify: postfix_restart
+  become: True

tasks/install.yml

@@ -1,5 +1,7 @@
 ---
 - name: Install postfix mta
+  block:
+  - name: Install required packages
     package:
       name: '{{ item }}'
       state: latest
@@ -7,3 +9,4 @@
       - postfix
       - cyrus-sasl-plain
       - mailx
+  become: True