In the member signup process under Creat account, it is possible to set Invite only to "Yes, admins must invite new members before they can signup".

/admin/user/signup/index/signup_id/1

Invite can only be sent 10 email address at a time. If you have hundreds of email to send, this could be a lenghty process. Also Invite code can be bound to each invited email address.

It would be nice to be able to use an invite code to automatically approve new members. This invite code could be sent via email (outside of the site) to a large list of emails. This would allow invitees to create an account using that general invite. It should be possible as well to change that invite key manually or have a time expiry for it.

Thanks,