No subscribing needed. Standard policy on all mailing lists is to reply-to-all so you'll get always CC'ed on replies. This also makes it very easy to pull in more people into a discussion, even across different projects.
Many mailing lists today reject posts from non-subscribers.
Of those that allow posts from non-subscribers, you will find that many are configured such that you will not get a reply, due to "reply-to munging". Your message will go to the list, but with a Reply-to: header designating that list, instead of (or in addition to) setting the more modern mailing-list-related headers.
Reply-to-all isn't a list policy; it's a behavior of the individuals. Some people don't reply to all. They think they are, but only the post author gets their reply. That is one of the motivations behind the Reply-to.
https://marc.merlins.org/netrants/reply-to-still-harmful.htm...