function sendEmails()
{
  var sheet = SpreadsheetApp.getActiveSheet();
  var activeRange = sheet.getActiveRange();
  var rows = sheet.getLastRow();
  var dataRange = sheet.getRange(1, 1, rows, 2);
  var data = activeRange.getValues();
  for (var i = 0; i < data.length; ++i)
  {
    var row = data[i];
    var name = row[1];
    var email = row[2];
    var subject = "Тема письма";
    var body = "Тест, " + name + "! проверка рассылки";
    MailApp.sendEmail(email, subject, body);
    sheet.getRange(i+1, 6).setValue("Отправлено");
    SpreadsheetApp.flush(); <span id="pastemarkerend"> </span>
  }
}

sheet.getRange(i+1, 6).setValue("Отправлено");