Allow bigger message size.

mail/docker-compose.yaml

@@ -49,6 +49,7 @@ services:
       - ENABLE_SPAMASSASSIN=1
       - SPOOF_PROTECTION=1
       - ENABLE_MANAGESIEVE=1
+      - POSTFIX_MESSAGE_SIZE_LIMIT=40960000
     healthcheck:
       test: "ss --listening --tcp | grep -P 'LISTEN.+:smtp' || exit 1"
       timeout: 3s