LH Disable BP Registration is a simple plugin that delivers an alternative to disabling registration via the Dashboard>>Settings>>General page.
The plugin creates an email blacklist area in the Dashboard>>Settings>>BuddyPress>>Options page allowing you to add the email domains you would like blacklisted. You can also set the rejection message and an extra message for the registration page explaining the restriction.
BuddyPress Registration Groups is a plugin that adds a list of groups to the registration form so that new members can be introduced and join your groups. It means they don’t need to go looking for them to be instantly tied in to their preferred groups. Adding this kind or form to your registration can help you to build a profile for each new member.