I made this service to replace mailman in a few sports club I'm member of: https://mailgroup.io . I've let it be free for anyone who wants to use it. Took a while to get all the deliverability stuff right, and all the monitoring in place, but we've been using it successfully for about 5 years now. I know it's not self hosted as you asked for, but thought I'd put it out there anyway, just in case a hosted free service would also be an option.