https://en.wikipedia.org/wiki/Usenet used to be the thing before forums took over. Every decent ISP would host a news server for their users.

As a user, you'd dial in, sync your newsreader software, and later whenever you want you can go through all the threads in the groups you're subscribed to and respond at your leisure. Your posts go out next time you sync up.

Could be worth looking at what worked and what failed over the various forms forums have taken over the years – email lists, usenet, web forums, etc.