diff --git a/docker-mailserver/docker-compose.yml b/docker-mailserver/docker-compose.yml
index b9784d5..e0bd113 100644
--- a/docker-mailserver/docker-compose.yml
+++ b/docker-mailserver/docker-compose.yml
@@ -11,6 +11,7 @@ services:
     # More information about the mailserver ports:
     # https://docker-mailserver.github.io/docker-mailserver/edge/config/security/understanding-the-ports/
     ports:
+      - "25:25"    # SMTP
       - "143:143"  # IMAP4 (explicit TLS => STARTTLS)
       - "465:465"  # ESMTP (implicit TLS)
       - "587:587"  # ESMTP (explicit TLS => STARTTLS)