I did some reading about majordomo. The current version is 1.94.5 and it's been that way for about 15 years. Brent Chapman, the original author of majordomo, stopped using majordomo (read down the comments till 17th October 2009) and moved to mailman.
I might do some more research into mailman, but I am still inclined to write my own simplified version based on majordomo. It's an itch I would like to scratch, and I would like to learn more.
I've written a lot of software for email. I have written software that sends about 50,000 emails a day at work. These are messages we take on the phone for our customers, and we transcribe the messages and email them to our customers. Obviously, every email is different so it's not spam, despite the volume. It's distributed, fast, follows all rules, works hard to be good email software and not cause any problems. I've written email parsers so inbound emails can be injected into our systems for our customers. I've written a lot of software to transport email around. I haven't done anything with mailing lists, and I think I should so I know at a deeper level what they do.