I have written a very simple plugin to make discourse to accept incoming emails over http rather than by polling an external mailbox. At first I though it would be simple enough that it would work across different mail services but in the end I opted to make it specific to Mailgun. Adapting it to work with Madrill or Sendgrid should be a less than 10 lines change.
Before you deploy this in production please be aware that I’m a total newbie at programming with Rails. Use it at your own risk! Also, I’d appreciate any any feedback you might have.