Some may see it as a violation of RFC to not return a DSN on failed delivery.
It seems reasonable to design a mail system so that notifications are sent back to the originator of the message when there is a problem somewhere along the delivery chain.
Others, like myself see the need to not return a failure notice on virus / trojan infected email as it has become the norm that the sender information is forged.
It seems very UNreasonable to send notifications to random destinations that have nothing to do with originating the message in question. The crux of the matter is that if you don't KNOW the true source of the message, then you cannot return a DSN. You can go through the motions, but then you are originating SPAM (UBE), not returning DSNs. Should you be accepting any mail at all from SMTP servers that you do not know and trust because of prior contact, i.e. negotiating an email peering agreement? --Michael Dillon