Create timestamp with script editor when email is sent
===

I am currently receiving data through an RSS feed into my spreadsheet. I have a script (below) which I am hoping to run on a time trigger (every minute) to check the data and then in turn send an email out if the data meets certain criteria. 

Problem: After the first email is sent out, I want to create a system to check (timestamp?) within the script if an email for that particular row of data has already been sent. Is this the best way to do this? How do I do it? Script is below.


    function sendEmail(email_address, email_subject, email_message) {
      MailApp.sendEmail(email_address, email_subject, email_message);
    }




    function test_sendEmail() {
      var sheet = SpreadsheetApp.getActiveSheet();
      var cell = sheet.setActiveCell('A2');
      var criterion_cutoff = 5;
      var i = 0;
      var addr;
      var subj;
      var msg;
      do {
        addr = cell.offset(i,0).getValue();
        subj = cell.offset(i,1).getValue();
        msg = cell.offset(i,2).getValue();
        criterion = cell.offset(i,3).getValue();
  
        if(criterion < criterion_cutoff) {
          sendEmail(addr,subj,msg);
          Browser.msgBox('Sending email to: ' + addr);
        }
        i++;
      } while( cell.offset(i, 0).getValue().length > 0 )
    
      Browser.msgBox('Done!');
    }