(function runMailScript(/* GlideRecord */ current, /* TemplatePrinter */ template, /* Optional EmailOutbound */ email, /* Optional GlideRecord */ email_action, /* Optional GlideRecord */ event) {

//Get the value of notes
var status = current.u_notes;

//call the function
errorReport(status);


 function errorReport(status){

 if (status >= 400 && status < 499) {

 template.print("<p>Client Error!</p>"); 

 } else if (status >= 500 && status< 599) {

 template.print("<p>Server Error!</p>"); 

 } else {

 template.print("<p>Error!</p>"); 

 }

 }
})(current, template, email, email_action, event);

Notification  body : 

HTTP Status: ${u_notes}

${mail_script:ErrorReportNotificationScript}