Oh I am so sorry abt misdirecting you. I am using MIME::Entity , which has compatibility with Mail::Internet, so that methods like smtpsend() will work. I dunno why the Sender header is being added. This doesn't happen when I use Mail::SendMail. But for other reasons I would like to use smtpsend albeit without the Sender header.
And really dumb of me to give the wrong link.