Rails - Aug 2009 - Actionmailer ignores return-path setting

Hello,

i have the problem that i want to set the return-path to the envelope
of outgoing emails so bounces can be handled. I tried to set the
header as followed in my mailer class:

  def newsletter
    subject       ''subject''
    reply_to     
''donotreply-9IKiO1iGCm/QT0dZR+AlfA@public.gmane.org''
    from         
''from-9IKiO1iGCm/QT0dZR+AlfA@public.gmane.org''
    recipients   ''to-d/KskAPSnHltswb4iDofSQ@public.gmane.org''
    sent_on       Time.now
    body          :body => ''content''
    headers       ''return-path'' =>
''donotreply-9IKiO1iGCm/QT0dZR+AlfA@public.gmane.org''
  end

However, in the outgoing email the return path is automatically set to
''from-9IKiO1iGCm/QT0dZR+AlfA@public.gmane.org''

I am using Rails 2.3.3 and Postfix 2.3

can anyone point me to the correct setting to set the return-path?

Greets
-act