she can revoke permission from everyone he has introduced her to, and take
 back his "Trusted Introducer" status. She can let him retain permission to
 send her mail independently of the introduction flag. She always has final
 control over her inbox, but the introduction feature removes the need for
 the CAPTCHA challenges to a bare minimum. With automatic introduction, most
 of the people in your address book can get permission without ever having to
 go through a Ticket Server.