var EMAIL_SENT = 'EMAIL_SENT';

function sendEmails() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2;
  var numRows = 2;
  var dataRange = sheet.getRange(startRow, 1, numRows, 3)
  var data = dataRange.getValues();
  for (i in data) {
   var row = data[i];
   var emailAddress = row[0];
   var message = "REJECTED LOAD NUMBER:  " + row[1] + row[2] + ",n";
   var subject = "REJECTED LOAD";
   var emailSent = row[2];
   if (emailSent != EMAIL_SENT) {
   MailApp.sendEmail(emailAddress, subject, message);
   sheet.getRange(startRow + i, 4).setValue(EMAIL_SENT);
    }
   }
  }