There's a guy that runs multiple sports teams at a local recreation center, in multiple adult divisions (wide age/culture rage), and he has been using email to great effect for over a decade that I have known him. I get 2-3 weekly emails about teams that need a sub for a game and those spots continue to fill up quickly. He probably has the majority of regulars (in the hundreds) at that sports center on his various email list. It just works. They tried chat groups once and that was a disaster.