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by QE2 5935 days ago
Many mail daemons will "accept" mail no matter who the recipient is. Internally, unmatched mail may be discarded or forwarded to a "catch-all" account, but all the sender sees is "Recipient ok"

I think this started as a response to SPAM bots that used to "RCPT TO:" random strings and save a list of valid address.

1 comments

Pretty sure that's a MUST NOT in the RFC