System.Web.Mail & Headers

[Dan___]

How to send a mailmessage with a return receipt?

I use the property Headers of the class MailMessage

dim myMail as new MailMessage
myMail.Headers.Add("Return-Receipt-To", <ad*****@mail.com>)
myMail.Headers.Add("Disposition-Notification-To", <ad*****@mail.com>)

The header "Disposition-Notification-To" run, not "Return-Receipt-To".
An idea?

Thanks