function onOpen(e) {
   SpreadsheetApp.getUi()
       .createMenu('SBS Mailer')
       .addItem('Send out emails', 'sendEmails')
       .addItem('Remaining quota', 'remainingQuota')
       .addToUi();
}

function remainingQuota() {
   var emailQuotaRemaining = MailApp.getRemainingDailyQuota();
   Logger.log("Remaining email quota: " + emailQuotaRemaining);
  
  var ss = SpreadsheetApp.openById("1sxOrLJM0Tvd-21vu2zfVxSOSd2lL-hKmYOppQJGDtT8");
  var sheet = ss.getSheetByName('emails_list');
  var quota = ss.getRange("F2").setValue(emailQuotaRemaining);
}

function sendEmails() {
  var ss = SpreadsheetApp.openById("1sxOrLJM0Tvd-21vu2zfVxSOSd2lL-hKmYOppQJGDtT8");
  var sheet = ss.getSheetByName('emails_list');
  var subject = ss.getRange("E2").getValue();
  
  var count_range = sheet.getRange(2, 1, 1500).getValues();
  var flat = count_range.reduce(function(acc, row){
    return acc.concat(row.filter(function(x) {
      return x != "";
    }));
  }, []);
  
  var startRow=2; 
  var numRows=flat.length;
  
  var dataRange=sheet.getRange(startRow, 1, numRows, 3);
  //changed to getDisplayValues
  var data=dataRange.getDisplayValues();
  //changed to for loop
  for (var i=0;i<data.length;i++) {
    var row=data[i];
    var emailAddress=row[0]; 
    
      
    var message=HtmlService.createHtmlOutputFromFile('mail_template').getContent();
    
    var options = {}
    options.htmlBody = message;
    MailApp.sendEmail(emailAddress, subject, '', options);

  }
}