returned eMails

Hi ! We have a site which send mails to customers regulary. My problem is that when some mails are returned (bacause addresses are not available or mailboxes are full etc..) they are returned to the server administrator and not to the sender of the message. When I send a mail, I use the PHP mail function . In the header I put "From: sender@domain.xxx\n\n" The "From" is ok because when someone receive the message, it is From the address I put. May be is there another field to put in the header for the refused messages are returned to the sender I want ? Thank you for your help jean-arthur ---------------------------------------------------------------- EuroVox 4, place Félix Eboue 75583 Paris Cedex 12 Tel : 01 44 67 05 05 Fax : 01 44 67 05 19 Web : http://www.eurovox.fr ----------------------------------------------------------------