diff --git a/templates/docker-compose/docker-compose.yml b/templates/docker-compose/docker-compose.yml
index f874bf3..6e3731f 100644
--- a/templates/docker-compose/docker-compose.yml
+++ b/templates/docker-compose/docker-compose.yml
@@ -251,6 +251,7 @@ services:
       MAIL_TO: nick@noodlefactory.co.uk
       MAIL_SUBJECT: Borgmatic Backup
       # MAIL_PASSWORD is set via volumes/borgmatic-config/msmtp.env, created via ansible
+      # Test SMTP auth on the server https://doc.dovecot.org/admin_manual/debugging/debugging_authentication/
     env_file:
       - ./borgmatic.env
       # FIXME create backup service