A good lightweight mail relay to relay unencrypted mail connections to a server that requires encryption?

I am developing against software app that sends notifications via email and it doesn't support SSL/TLS encryption. I need to send these notifications to a server that only supports encrypted connections.

I am thinking about I might be able to solve these problems with a local mail relay, something that runs as a windows service and accepts local unencrypted connections then relays the mail to the proper server using an encrypted开发者_开发问答 connection.

Does anyone know of a good lightweight mail relay/server app that I can use to do this? Is there a better solution?

I've had some great success with hMailServer - I think it covers your needs (I'm using it as a small domain mailserver).