diff --git a/tasks/main.yml b/tasks/main.yml
index b74c99c..e793faa 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -32,6 +32,7 @@
   ansible.builtin.include_tasks: mta-sts.yml
   tags: mta-sts
   loop: "{{ postfix_domains }}"
+  when: postfix_domains is defined
   args:
     apply:
       delegate_to: "{{ gateway_host }}"