Is there a way to automatically do this? Or do they have to manually opt in? We are looking for an equivalent of inviting your Facebook friends to like your business's Facebook page. They receive a notification telling them they've been invited to like the page. Similarly we'd like our list members to receive a notice saying they've been invited to join the group. They just need to accept.
I've done a little searching and most of the solutions proposed seem dated. Some of the features referred to no longer exist!