Awesome
docker-mailcatcher
This docker container can be use to send emails via SMTP and route all incoming SMTP traffic to a single mailbox which can be accessed via IMAP.
You can also access the mailbox via the webmail service which is exposed on port 80.
Example Run
docker run -d \
-e MAILCATCHER_USERNAME=mailcatcher \
-e MAILCATCHER_PASSWORD=mailcatcher \
hauptmedia/mailcatcher