It is a very small image (~34 MB uncompressed) available on docker hub based on Alpine Linux and using the last available release from the official Github repo of [MailHog][mailhog].
Get it:
git clone https://github.com/dcnl1980/docker-mailcatcher.git
Build it:
docker-compose build
Run it:
docker-compose up
Then you can send emails from your app to port 1025 and check out the web interface: http://<your docker host>:1080/. Or link this container to your webdevelopment container.