This is a simple SMTP server listener which processes any incoming SMTP message, and forwards it to the specified url as a POST request.
See example_store.php for an example on how to process the incoming message.
See example_nginx.conf for an example on how to configure nginx to use STARTTLS,
and forward it to the node.js server.
If TLS or nginx is not wanted, server port can be changed
from 2525 to 25 to expose it to the internet directly.