title: Block emails with large number of recipients of same domain
body: <p>I have a mailserver with exim4 and spamassassin installed.</p>
  
  <p>We have a problem of (internal) spam to a large number of mailinglists, coming from a few  users (which we cannot just educate or block for multiple reasons)</p>
  
  <p>Is there a way to block emails to which an unreasonable amount go to the same domain (e.g. 10) to force these users to BCC?</p>