BuddyPress.org

“It’s possible to add a “I dont want to receive more invites” on each email? (like a unsubscribe link). This will solve a lot of headaches if someone start receive multiple invites from a lot of people.”

Actually something like this might be required by the Can Spam act. Not for sure of the details. I think we need to look at one of the Facebook emails and see what they have since certainly they’ve gone through a lot more work and effort to figure out how to send emails like this in large quantities.