diff --git a/roles/docker/tasks/services/postfix.yml b/roles/docker/tasks/services/postfix.yml
index c565686..0959556 100644
--- a/roles/docker/tasks/services/postfix.yml
+++ b/roles/docker/tasks/services/postfix.yml
@@ -16,5 +16,5 @@
       - name: postfix
     env:
       # Get all services which have allowed_sender_domain defined
-      ALLOWED_SENDER_DOMAINS: "{{ services | dict2items | selectattr('value.allowed_sender_domain', 'defined') | map(attribute='value.domain') | list | join(' ') }}"
+      ALLOWED_SENDER_DOMAINS: "{{ services | dict2items | selectattr('value.allowed_sender_domain', 'true') | map(attribute='value.domain') | join(' ') }}"
       HOSTNAME: "smtp.data.coop" # the name the smtp server will identify itself as