Continued struggling with mailing list services, but I eventually settled on a solution
Ultimate solution: Topicbox + a custom, separate domain
First, I want a custom domain because I want to be able to change mailing list vendors without updating all my alias email addresses (e.g., I don’t want devs@tinypilot.topicbox.com)
Initially, I was trying to use a tinypilotkvm.com subdomain like lists.tinypilotkvm.com, but the problem was that even with a separate MX record for lists.tinypilotkvm.com, Fastmail (my main mail provider for tinypilotkvm.com) thinks that it owns all subdomains, so it would get confused when I try to respond to messages at subdomains because it thinks it doesn’t have to route the message externally (even when I set it to route externally)
I also tried Gaggle, but I ran into the same issues.
I eventually just created a whole dedicated domain for group emails so there’s no confusion with Fastmail