code: static function sortEmailsByCreationDatePredicate($emailA, $emailB) 
    {
      $sortKeyA = $emailA->sent_at;
      $sortKeyB = $emailB->sent_at;
      return ($sortKeyA > $sortKeyB) ? -1 : 1;
    }
docs: Get Email To
  
  Returns the string containing the persons included in the To field
  
  @param mixed $emailA Email
  @param mixed $emailB Email
  @return int Which email should go first