Vb.net 使用smtpserver时请求在电子邮件上读取回执

我成功地使用smtpserver发送电子邮件。我正在编写一个VB.Net应用程序

我目前的代码是：

    SmtpServer.Credentials = New Net.NetworkCredential(mEMailUser, mEMailPassword) 
    SmtpServer.Port = 587 
    SmtpServer.Host = mHostName 
    mail = New MailMessage() 
    mail.From = New MailAddress(mFromEMail) 
    mail.To.Add(mfrmSendAnEmail.txtTo.Text) 
    mail.Subject = mfrmSendAnEmail.txtSubject.Text 

    _Attachment = mDirectory & "\" & gcloGlobals.DocumentName & ".pdf" 
    Dim oAttch As Attachment = New Attachment(_Attachment) 
    mail.Attachments.Add(oAttch) 

    mail.Body = mfrmSendAnEmail.txtBody.Text 
    SmtpServer.Send(mail) 

我希望收件人收到读取请求通知，这样当他们打开电子邮件时，他们可以选择向发件人发送已读取的通知

我想这可能有用：

  mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnSuccess

但它没有。以下是我使用的代码：

message.Headers.Add("Disposition-Notification-To", "\"" + fromAddress.DisplayName + "\" <" + fromAddress.Address + ">");

以下是我使用的代码：

message.Headers.Add("Disposition-Notification-To", "\"" + fromAddress.DisplayName + "\" <" + fromAddress.Address + ">");