Young Adults Message Board › mass group emailing
please try to keep emails to (all) group members to a minimum to respect people's personal space. If it ends up being some special event meetup it'd be okay to announce it once ahead of time and then later the day before or day of. But generally there is not a need to email to everyone in the group.
Emailing to people who have RSVP'd to an event is something completely different though as they would probably like to be kept appraised of what's going on.
Ultimately if people want to get involved they are most likely to be browsing the meetup page anyhow.