If points equal value: reset to zero
Download the Rules module and import the following rule:

{ "rules_reset_points" : {
    "LABEL" : "Reset points",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "TAGS" : [ "Points" ],
    "REQUIRES" : [ "php", "rules", "userpoints_rules" ],
    "ON" : { "userpoints_event_points_awarded_after" : [] },
    "IF" : [
      { "php_eval" : { "code" : "global $user;\r\n$num_pts = userpoints_get_current_points($user-\u003Euid, \u0027all\u0027);\r\nif ($num_pts \u003E 100) {return TRUE;}" } }
    ],
    "DO" : [
      { "userpoints_rules_get_current_points" : {
          "USING" : { "user" : [ "userpoints-transaction:user" ], "tid" : "all" },
          "PROVIDE" : { "loaded_points" : { "loaded_points" : "Number of points in the specified category." } }
        }
      },
      { "data_calc" : {
          "USING" : { "input_1" : [ "loaded-points" ], "op" : "*", "input_2" : "-1" },
          "PROVIDE" : { "result" : { "result" : "Calculation result" } }
        }
      },
      { "userpoints_action_grant_points" : {
          "user" : [ "userpoints-transaction:user" ],
          "points" : [ "result" ],
          "tid" : "0",
          "entity" : [ "" ],
          "description" : "Prevent more than 100 points.",
          "operation" : "Add",
          "display" : 0,
          "moderate" : "approved"
        }
      }
    ]
  }
}


Adapt the actions to your needs, add another action "Send mail" after installing the Mime mail module (this article may help you in doing that) and you're done!