BulkWatch is a utility that monitors sendmail's
logs and takes a specified action when an IP has
exceeded your configured maximum settings. You can
specify that users may send X messages in X number
of seconds. Email in excess of that would trigger
an action, which can be any of the following:
display an alert to the screen in foreground mode;
log an alert to syslog; email an alert to a
predefined email address; or run an external
command with the IP and number of messages as
arguments.