sendMails.gs

var sheet = SpreadsheetApp.getActiveSheet();

function Account(_id, _name, _email, _isSend) {
  this.id = _id;
  this.name = _name;
  this.email = _email;
  var isSend = _isSend; // private scope
  
  this.isSend = function() { return isSend === "SENDED" ? true : false; };
  this.isNotSend = function() { return isSend !== "SENDED" ? true : false; };
}

var AccountFactory = {
  createAccount: function(id, account) {
    return new Account(id, account[0], account[1], account[2]);
  }
};

function getEmails() {
  var startRow = 2,
      numRows = 2,
      dataRange = sheet.getRange(startRow, 1, numRows, 3),
      data = dataRange.getValues();
  var i = startRow;
  
  return data.map(function(account) { return AccountFactory.createAccount(i++, account); });
}

function sendEmails(accounts) {
  accounts.forEach(function(account) {
    if (account.isNotSend()) {
      MailApp.sendEmail(account.email, "ทดลองส่งผ่าน AppScript", "สวัสดีครัช " + account.name + " มีความพยายาม แต่ก็ยังอ่อนหัด!!!");
      
      sheet.getRange(account.id, 3).setValue("SENDED");
      SpreadsheetApp.flush();
    }
  });
}

function main() {
  var accounts = getEmails();
  sendEmails(accounts);
}