With Google Docs, you can send personalized email in rich-text HTML format to a large group of people using Mail Merge. This snippet of Google Apps Script is responsible for sending the messages.

function labnolSendEmail() {
  var mySheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();

  var emailSubject = mySheet.getRange('E5').getValue();
  var emailSalutation = mySheet.getRange('E7').getValue();
  var emailBody = mySheet.getRange('E9').getValue();
  var emailYourName = mySheet.getRange('E11').getValue();
  var emailYourAddr = Session.getUser().getEmail();
  var replyToAddr = mySheet.getRange('E13').getValue();
  var file = mySheet.getRange('E15').getValue();
  var attachmentID = file ? DocsList.getFileById(file) : '';
  var emailBCC = mySheet.getRange('E17').getValue();

  var myContact = mySheet.getDataRange().getValues();

  for (i = 1; i < myContact.length; i++) {
    var person = myContact[i];
    if (person[0] != '' && person[1] != '' && person[2] != 'OK') {
      var emailMsg = emailSalutation + ' ' + person[0] + ', <br />' + emailBody;
      var advancedArgs = { htmlBody: emailMsg, name: emailYourName, replyTo: replyToAddr };

      if (file) advancedArgs['attachments'] = attachmentID;

      if (emailBCC == 'YES') advancedArgs['bcc'] = emailYourAddr;

      GmailApp.sendEmail(person[1], emailSubject, emailMsg, advancedArgs);

      mySheet.getRange(i + 1, 3).setValue('OK');
    }
  }
}