I try to use this option
: d meaning (from the help file)
dsn ââ,¬â€œ Request delivery status notification (request a delivery receipt from the receiving server). (NB: This feature must be enabled on the mail server for this request to work.) Emails sent with the dsn request will contain "Return-Receipt-To:" in the header.
May be I don't search well enough, but I found nowhere to specify this info : "Return-Receipt-To:" , could someone help me please
The help file text is telling you that the extender adds the header automagically.