diff --git a/roles/mail_forwarder/defaults/main.yml b/roles/mail_forwarder/defaults/main.yml
index 9aff8c79653f0a08fcfe6f90e58a3df916df6f63..e7dcda4ed297d54c66f03a91194cc5814bfdbc15 100644
--- a/roles/mail_forwarder/defaults/main.yml
+++ b/roles/mail_forwarder/defaults/main.yml
@@ -1,7 +1,7 @@
 ---
 
 local_mail_aliases: {}
-smtp_from_relay_allowed: True
+smtp_from_relay_allowed: true
 smtp_relay_host: ""
 smtp_relay_truststore: "{{ lookup('file', tls_certificate_dir + '/truststore.pem') }}"
 smtp_relay_host_port: null
diff --git a/roles/mail_forwarder/molecule/default/create.yml b/roles/mail_forwarder/molecule/default/create.yml
index f8eb37cd4df02c540216c02791d0c50870986202..ce8657f9bae3be7f42731fd1efe77e87a62afcd9 100644
--- a/roles/mail_forwarder/molecule/default/create.yml
+++ b/roles/mail_forwarder/molecule/default/create.yml
@@ -2,7 +2,7 @@
 - name: Create
   hosts: localhost
   connection: local
-  gather_facts: False
+  gather_facts: false
   no_log: "{{ not lookup('env', 'MOLECULE_DEBUG') | bool }}"
   vars:
     molecule_file: "{{ lookup('env', 'MOLECULE_FILE') }}"
diff --git a/roles/mail_forwarder/molecule/default/destroy.yml b/roles/mail_forwarder/molecule/default/destroy.yml
index 3972a2df8fafe515b30a74f951499b83aae8449c..8f0a3703672765e77f4f1a3a8046a1f2b561a7a8 100644
--- a/roles/mail_forwarder/molecule/default/destroy.yml
+++ b/roles/mail_forwarder/molecule/default/destroy.yml
@@ -3,7 +3,7 @@
 - name: Destroy
   hosts: localhost
   connection: local
-  gather_facts: False
+  gather_facts: false
   no_log: "{{ not lookup('env', 'MOLECULE_DEBUG') | bool }}"
   vars:
     molecule_file: "{{ lookup('env', 'MOLECULE_FILE') }}"
diff --git a/roles/mail_forwarder/molecule/default/group_vars/parameters-mandatory.yml b/roles/mail_forwarder/molecule/default/group_vars/parameters-mandatory.yml
new file mode 100644
index 0000000000000000000000000000000000000000..9dca40540130109a6cb72761f1249bb3c194113a
--- /dev/null
+++ b/roles/mail_forwarder/molecule/default/group_vars/parameters-mandatory.yml
@@ -0,0 +1,4 @@
+---
+
+# Global common parameters.
+tls_certificate_dir: tests/data/x509/
diff --git a/roles/mail_forwarder/molecule/default/group_vars/parameters-no-incoming.yml b/roles/mail_forwarder/molecule/default/group_vars/parameters-no-incoming.yml
new file mode 100644
index 0000000000000000000000000000000000000000..3630e68710c6bd70c8b073d0f6bfa9c94a22679e
--- /dev/null
+++ b/roles/mail_forwarder/molecule/default/group_vars/parameters-no-incoming.yml
@@ -0,0 +1,9 @@
+---
+
+smtp_relay_host: mail-server
+smtp_from_relay_allowed: false
+smtp_relay_truststore: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
+
+# common
+ca_certificates:
+  testca: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
diff --git a/roles/mail_forwarder/molecule/default/group_vars/parameters-optional.yml b/roles/mail_forwarder/molecule/default/group_vars/parameters-optional.yml
new file mode 100644
index 0000000000000000000000000000000000000000..cc643b03c25e1630886fd286648f466ba9ac4260
--- /dev/null
+++ b/roles/mail_forwarder/molecule/default/group_vars/parameters-optional.yml
@@ -0,0 +1,12 @@
+---
+
+local_mail_aliases:
+  root: "root testuser"
+smtp_from_relay_allowed: true
+smtp_relay_host: mail-server
+smtp_relay_host_port: 27
+smtp_relay_truststore: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
+
+# common
+ca_certificates:
+  testca: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
diff --git a/roles/mail_forwarder/molecule/default/molecule.yml b/roles/mail_forwarder/molecule/default/molecule.yml
index cf0918496f88fe2b4719810bd6fcec4a81dd56a8..913d73e7edee357aa900bc1ad432120811aeda3e 100644
--- a/roles/mail_forwarder/molecule/default/molecule.yml
+++ b/roles/mail_forwarder/molecule/default/molecule.yml
@@ -9,6 +9,8 @@ driver:
 
 lint:
   name: yamllint
+  options:
+    config-file: ../../.yamllint.yml
 
 platforms:
 
diff --git a/roles/mail_forwarder/molecule/default/playbook.yml b/roles/mail_forwarder/molecule/default/playbook.yml
index 997a28c7bc51b15aebd874fb8ebf4ebbdcad2912..60ff856f3fa8872ff79627c723791b8435653e45 100644
--- a/roles/mail_forwarder/molecule/default/playbook.yml
+++ b/roles/mail_forwarder/molecule/default/playbook.yml
@@ -1,36 +1,6 @@
 ---
 
-- hosts: parameters-mandatory
-  become: yes
+- hosts: parameters-mandatory,parameters-optional,parameters-no-incoming
+  become: true
   roles:
-    - role: mail_forwarder
-
-      # Global common parameters.
-      tls_certificate_dir: tests/data/x509/
-
-- hosts: parameters-optional
-  become: yes
-  roles:
-    - role: mail_forwarder
-      local_mail_aliases:
-        root: "root testuser"
-      smtp_from_relay_allowed: True
-      smtp_relay_host: mail-server
-      smtp_relay_host_port: 27
-      smtp_relay_truststore: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
-
-      # common
-      ca_certificates:
-        testca: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
-
-- hosts: parameters-no-incoming
-  become: yes
-  roles:
-    - role: mail_forwarder
-      smtp_relay_host: mail-server
-      smtp_from_relay_allowed: False
-      smtp_relay_truststore: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
-
-      # common
-      ca_certificates:
-        testca: "{{ lookup('file', 'tests/data/x509/ca.cert.pem') }}"
+    - mail_forwarder
diff --git a/roles/mail_forwarder/molecule/default/prepare.yml b/roles/mail_forwarder/molecule/default/prepare.yml
index faacc4fd4b8028334693993f3e7c6aa40a801e74..b4dbf17b1d43eaea73a941f62e5e3282f3074511 100644
--- a/roles/mail_forwarder/molecule/default/prepare.yml
+++ b/roles/mail_forwarder/molecule/default/prepare.yml
@@ -2,24 +2,24 @@
 
 - name: Prepare
   hosts: all
-  gather_facts: False
+  gather_facts: false
   tasks:
     - name: Install python for Ansible
       raw: test -e /usr/bin/python || (apt -y update && apt install -y python-minimal)
-      become: True
-      changed_when: False
+      become: true
+      changed_when: false
 
 - hosts: all
-  become: yes
+  become: true
   tasks:
 
     - name: Update all caches to avoid errors due to missing remote archives
       apt:
-        update_cache: yes
-      changed_when: False
+        update_cache: true
+      changed_when: false
 
 - hosts: all
-  become: yes
+  become: true
   tasks:
 
     - name: Set-up the hosts file
@@ -42,18 +42,18 @@
         10.31.127.32: "parameters-no-incoming-stretch64"
 
 - hosts: clients
-  become: yes
+  become: true
   tasks:
 
     - name: Install SWAKS for testing SMTP capability
       apt:
         name: swaks
-        state: installed
+        state: present
 
     - name: Install tool for testing TCP connectivity
       apt:
         name: hping3
-        state: installed
+        state: present
 
     - name: Deploy CA certificate
       copy:
@@ -71,7 +71,7 @@
       command: /usr/sbin/update-ca-certificates --fresh
 
 - hosts: mail-servers
-  become: yes
+  become: true
   tasks:
 
     - name: Deploy CA certificate
@@ -96,10 +96,15 @@
         - mail-server_smtp.key.pem
 
     - name: Install Postfix
-      apt: name="postfix" state=installed
+      apt:
+        name: "postfix"
+        state: present
 
     - name: Purge Exim configuration
-      apt: name="exim4*" state=absent purge=yes
+      apt:
+        name: "exim4*"
+        state: absent
+        purge: true
 
     - name: Deploy Postfix configuration
       copy:
@@ -114,16 +119,16 @@
     - name: Install tool for testing TCP connectivity
       apt:
         name: hping3
-        state: installed
+        state: present
 
     - name: Install SWAKS for testing SMTP capability
       apt:
         name: swaks
-        state: installed
+        state: present
 
     - name: Set-up port forwarding
       command: "iptables -t nat -A PREROUTING -p tcp -m tcp --dport 27 -j REDIRECT --to-ports 25"
-      changed_when: False
+      changed_when: false
 
   handlers:
 
@@ -136,7 +141,7 @@
         state: restarted
 
 - hosts: parameters-optional
-  become: yes
+  become: true
   tasks:
 
     - name: Create additional group for testing local aliases
diff --git a/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_client.py b/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_client.py
index 62733713a5bdc949f51766c5887a7a8fa9d2a13e..a4679f27edb4e6fee17257b2eacb4a759d977c6f 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_client.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_client.py
@@ -1,8 +1,10 @@
+import os
+
 import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts('client1')
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['client1'])
 
 
 def test_connectivity_from_client(host):
diff --git a/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_relay.py b/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_relay.py
index 3adfea1b8cf2a3436791b94973a028602a2f6aec..bb6e068cc793c8982137b7c1f9e55983a8d3840a 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_relay.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_connectivity_from_relay.py
@@ -1,8 +1,10 @@
+import os
+
 import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts('mail-server')
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['mail-server'])
 
 
 def test_connectivity_from_relay(host):
diff --git a/roles/mail_forwarder/molecule/default/tests/test_default.py b/roles/mail_forwarder/molecule/default/tests/test_default.py
index a55c93a315e96e75b2f55118557f01a32fff4c05..5354fbadab08c7ac33c51f2cf3abc547239af2ae 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_default.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_default.py
@@ -1,8 +1,10 @@
+import os
+
 import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts(['parameters-mandatory', 'parameters-optional', 'parameters-no-incoming'])
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['parameters-mandatory', 'parameters-optional', 'parameters-no-incoming'])
 
 
 def test_installed_packages(host):
diff --git a/roles/mail_forwarder/molecule/default/tests/test_mandatory.py b/roles/mail_forwarder/molecule/default/tests/test_mandatory.py
index c9ca762319df39de9bcdea25bcebbece2b99698c..fbb3f090a5ca8a7e1d88e4fe0c0e4e7bacddd04d 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_mandatory.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_mandatory.py
@@ -1,12 +1,12 @@
+import os
 import re
 import time
 
-
 import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts('parameters-mandatory')
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['parameters-mandatory'])
 
 
 def test_smtp_relay_truststore_file(host):
diff --git a/roles/mail_forwarder/molecule/default/tests/test_optional.py b/roles/mail_forwarder/molecule/default/tests/test_optional.py
index f1661e45088c95c2544e7c38ac75e79f47f23ef0..1b9dc0a81f3bb9ff8c35daf315100bf6324a3fa7 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_optional.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_optional.py
@@ -1,12 +1,12 @@
+import os
 import re
 import time
 
-
 import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts('parameters-optional')
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['parameters-optional'])
 
 
 def test_smtp_relay_truststore_file(host):
diff --git a/roles/mail_forwarder/molecule/default/tests/test_smtp_relay_host_port.py b/roles/mail_forwarder/molecule/default/tests/test_smtp_relay_host_port.py
index e303f7fdd05be0d1e534929fc854bfcecd628006..165c0ac938fbc1f6c4c979af8cd5f25489e1769e 100644
--- a/roles/mail_forwarder/molecule/default/tests/test_smtp_relay_host_port.py
+++ b/roles/mail_forwarder/molecule/default/tests/test_smtp_relay_host_port.py
@@ -1,3 +1,4 @@
+import os
 import re
 import time
 
@@ -6,7 +7,7 @@ import testinfra.utils.ansible_runner
 
 
 testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
-    '.molecule/ansible_inventory.yml').get_hosts('parameters-no-incoming')
+    os.environ['MOLECULE_INVENTORY_FILE']).get_hosts(['parameters-no-incoming'])
 
 
 def test_postfix_main_cf_file_content(host):
diff --git a/roles/mail_forwarder/tasks/main.yml b/roles/mail_forwarder/tasks/main.yml
index 2b397b9df02ced774c01fab71b1f40f51bf5301a..6e85ef70fda13c8cafae7e18d6caee3aaaad92ac 100644
--- a/roles/mail_forwarder/tasks/main.yml
+++ b/roles/mail_forwarder/tasks/main.yml
@@ -3,18 +3,18 @@
 - name: Install Postfix
   apt:
     name: postfix
-    state: installed
+    state: present
 
 - name: Install procmail
   apt:
     name: procmail
-    state: installed
+    state: present
 
 - name: Purge Exim configuration
   apt:
     name: "exim4*"
     state: absent
-    purge: yes
+    purge: true
 
 - name: Deploy the SMTP relay TLS truststore
   copy:
@@ -77,7 +77,7 @@
 - name: Install SWAKS
   apt:
     name: swaks
-    state: installed
+    state: present
 
 - name: Explicitly run all handlers
   include: ../handlers/main.yml