[Answered ]-Debugging 500 on incoming Mail on Heroku from Mailgun

I finally figured out what the problem was:

1) in the Mailgun tutorial, the route you create doesn’t have a ‘/’ at the end (example is: http://myhost.com/messages) – however, APPEND_SLASH caused problems for the POST redirect then. The solution is to simply append the ”/’ at the end for the redirect

2) (potential further issue later in production) – do note that in Django 1.5 the allowed_host value was introduced which restricts the domains which are allowed to make POST requests. I believe this is only used in production environments (debug = false) but could cause problems later so make sure that you set these accordingly as well (I believe to allow mailgun.org as host).

Thanks to everybody who tried to help out!