m242/Maildrop
A couple days ago, some colleague of mine asked me to set up our own Maildrop service, as served by maildrop.cc. Some of you may also be familiar with Mailinator, which offers with a similar service.
Note to be confused with Maildrop (popular MDA, as distributed in Debian packages, among others, …) m242/Maildrop is based on Scala, Java and a Redis queue. The project is divided into two workers connecting to Redis.
maildrop
An SMTP worker would be processing inbound messages, eventually writing them to Redis. Listening on 127.0.0.1:25000 by default, nginx may be used proxying traffic.
Meanwhile, the HTTP worker would serve clients with any mailbox – no authentication required. Developers may write tests checking for some arbitrary mailbox using some HTTP API.
As you may guess: both workers and database may be scaled horizontally. Although being a pretty specific implementation, you probably won’t need it to.
Their GitHub project isn’t much active, sadly. A few issues piling up, two of which I’ve been able to post pull requests for. Then again, getting it working isn’t much complicated, and may prove pretty useful testing for regressions.