diff --git a/compose.mailrelay.yml b/compose.mailrelay.yml
index ad686d8..8d89168 100644
--- a/compose.mailrelay.yml
+++ b/compose.mailrelay.yml
@@ -6,6 +6,7 @@ services:
     entrypoint: /docker-entrypoint.mailrelay.sh
     environment:
       - SMTP_HOST=${SMTP_HOST}
+      - SMTP_PORT=${SMTP_PORT}
       - MAIL_FROM=${MAIL_FROM}
     configs:
       - source: mstmp_conf