If you don’t want Return Receipt

Notes does not have the feature to deny Return Receipt. If you don't like it you can disable it on the server

In the Configuration Settings > MIME tab > Conversion Options  tab > General tab, set "Return receipts" as Enabled or Disabled to affect how return receipts go to and from the Internet.  For more information, refer to the Domino Administrator Information Center topic "Enabling Domino to process return receipts for SMTP messages."

If you want to send but control Return Receipt on the Notes Client put the code on the QueryOpen event of the memo form:

Dim answer As Integer
       If( Not Source.Document Is Nothing ) Then
               If( Source.Document.HasItem( "ReturnReceipt" ) ) Then
                       If( Source.Document.ReturnReceipt(0) = "1" ) Then
                               answer% = Messagebox("Deseja enviar aviso de recebimento solicitado por"& Chr$(10) & Chr$(13) & Chr$(13)_
                               &Source.Document.GetItemValue("From")(0), 36, _
                               "Aviso de Recebimento")
                               If (answer%=7) Then
                                       Source.Document.ReturnReceipt = "0"
                                       Source.Document.Save True, False
                               End If
                       End If
               End If
       End If