The End-Systems table can be filtered to help manage access control.
Filter the State column to show the Rejected devices or Disconnected devices. And then filter again on the Last Seen column to filter by date (before or after) which could be useful to do when purging old entries. The list can be filtered based on Authentication Type ie MAC.
If you want to trigger an email based on a specific event go to Control>Access Control>Configuration>Notifications. You can add a new condition that will generate an email to a helpdesk for example.
Notifications can send an email if triggered, or execute a workflow, syslog event or script.