/etc/mailway/frontline/nginx.conf uncomment the bock that starts with
listen 0.0.0.0:587 ssl;.
Then restart the service:
It’s recommended to encrypt traffic to the port 25 as well by uncommenting the comments in the first block.
openssl s_client -connect $DOMAIN:587
$DOMAIN with the name of the domain you configured to receive emails.
If at the bottom you can read
220 $DOMAIN ESMTP ready it means that you successfully etablished a secure connection to the mail server. At the top you can find informations about the certificate.