In this repo, I've mushed together mailprotector/haraka-plugin-queue-rails and instrumentisto/haraka-docker-image so I can forward emails into a rails app.
You can use this image with the following ENV's (example values provided)
USER_AGENT=haraka
ACTION_MAILBOX_PASSWORD=superdupersecretpassword
ACTION_MAILBOX_URL=https://yourapp.com/rails/action_mailbox/relay/inbound_emails
HOSTNAME=inboundmail.yourapp.com
ACCEPT_MAIL_FOR_HOSTNAME=yourapp.com
See the original README's for more information