I wrote a tutorial last year that explained how to customize the Mailboxer Ruby gem and it was well-received. Many people requested source code so that they could debug issues. I unfortunately did not have the availability to provide the source code at the time. However, I am very happy to announce that an open source application is currently available on Github and it is completely free to use. A live demo of the app is also available on Heroku. I hope this helps anyone that is struggling to get mailboxer up and running in their Rails app! As always, feel free to ask questions if you run into issues.