Q:

Mark each row as successful after running google script

I have written a script that sends emails using a google sheet. Everything works properly, except marking the third column as successful. The first successful email is marked EMAIL_SENT, but none of the following cells are changed. Any ideas why this doesn't work?
for (row = 1; row < emailLength && confirmation == ui.Button.YES; row++){

  var customerEmail = data[row][0]; // Customer's email in first column

  var customerName = data[row][1]; // Customer's name in second column

  var EMAIL_SENT = 'Success';

  if(customerName != ''){

      var body = '<font face="avenir" size="3"> Hi '+ customerName + ',<br><br>' 
      + paragraphOne + '<br><br>'
      + paragraphTwo + '<br><br>'
      + paragraphThree + '<br><br>'
      + signature;
    }

  GmailApp.sendEmail(customerEmail, emailSubject, "", {htmlBody: body});

  sheet.getRange(row, 3).setValue(EMAIL_SENT);
}
};

A:

@bardo was on the right track. The issue was with getRange. With the way the code was originally, getRange(row, 3) was starting off on the third column and the first row. I wanted it to start off on the second row. data[row][x] was fine because those are indexes, but getRange needed to be getRange(row + 1 , 3)
  sheet.getRange(row + 1, 3).setValue(EMAIL_SENT);

