diff --git a/tasks/main.yml b/tasks/main.yml
index 80cd390..ed9d5b6 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -48,7 +48,7 @@
         hash:/etc/postfix/{{ d }}_users
         {% endif %}{{ '' if loop.last else ',' }}{% endfor %},
       VIRTUAL_TRANSPORT: "lmtp:{{ dovecot_container }}:24"
-      VIRTUAL_MAILBOX_DOMAINS: "{{ postfix_mail_domains }}"
+      VIRTUAL_MAILBOX_DOMAINS: "{{ postfix_mail_domains | join (', ') }}"
       SMTPD_SASL_PATH: "inet:{{ dovecot_container }}:12345"
       SMTPD_SASL_TYPE: dovecot
       SMTPD_SASL_AUTH_ENABLE: "{{ 'yes' if postfix_enable_smtpd_auth else 'no' }}"