Zend_Mail provides several methods to set additional Mail Headers:

• setReplyTo($email, $name=null): sets the Reply-To: header.

• setDate($date = null): sets the Date: header. This method uses current time stamp by default. Or You can pass time stamp, date string or Zend_Date instance to this method.

• setMessageId($id = true): sets the Message-Id: header. This method can generate message ID automatically by default. Or You can pass your message ID string to this method. This method call createMessageId() internally.

Note: Return-Path
If you set Return-Path on your mail, see Configuring sendmail transport. Unfortunately, setReturnPath($email) method does not perform this purpose.

Furthermore, arbitrary mail headers can be set by using the addHeader() method. It requires two parameters containing the name and the value of the header field. A third optional parameter determines if the header should have only one or multiple values: