[Compose] Add net_bind_service to Postfix container caps

docker-compose.yml

@@ -199,6 +199,8 @@ services:
         - DBNAME=${DBNAME}
         - DBUSER=${DBUSER}
         - DBPASS=${DBPASS}
+      cap_add:
+        - NET_BIND_SERVICE
       ports:
         - "${SMTP_PORT:-25}:25"
         - "${SMTPS_PORT:-465}:465"