Ask HN: What is a modern-day alternative to a Majordomo mailing list?

I have a requirement to set up a private email list for around 20 users. I have a Linode server on which to self-host the software. Many, many years ago, I used to run a Majordomo mailing list, so I am looking for something similar. It needs to be completely email controlled -- e.g. you can subscribe, unsubscribe and post via email. Web interface is not required. Open source preferred.