Kee mailed me off-list and correctly pointed out that much of what I was
saying wasn't really relevant.
But part of his response is on topic so I've taken the liberty of bringing
it back to the list.
on the specific issue (response to RCPT TO <non-existent-rcpt>) we were
discussing. It's clear that some operators can do this on very large
distributed systems. Others can't - or won't.
It could well be a "won't". By deferring the reject until after the
DATA command you make it very difficult to probe for valid addresses
to spam.
No, you don't make it difficult for spammers. They will send some data.
You only make it difficult for people attempting to verify addresses
without sending data; so-called "SMTP callback" for instance, or when
trying to verify a list of addresses for research purposes :-)
--
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