John Levine wrote:
For instance, what would happen if mail servers provided feedback to
both senders (on a per message basis in the form of NDNs)
Well, since 95% of all mail is spam, and all the spam has fake return
addresses, you'd increase the amount of bogus NDNs by more than an
order of magnitude. No thanks.
I should clarify. The way to notify the sender is for the check to be
done at SMTP time, and for the rejecting SMTP server to issue a 5xx SMTP
response to RCPT for that recipient. This should result in an NDN to be
sent to the sender for legitimate mail. It will result in an NDN for
spam only when the spam is submitted through somebody's MTA before being
sent to the MX for the recipient.
Incidentally, on a bad day I already get 400,000 NDNs from mail that I
didn't send, just from the minority of MTAs that send NDNs in response
to spam now. This is not a hypothetical problem.
Agreed, it's a very real - and huge - problem.
Keith
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