- added 5 second delay before responding to POP or SMTP
  client regarding invalid username or password attempt (limit number of
  effective brute force hack attempts per minute).
-  increment the user email sent statistics for authenticated SMTP msg recvs
- check the configured max emails per day value (for the user's security level)
  and reject any messages that would exceed this value (exept for 'M'-exempt
  users) - this has been on the todo list for a long time.