In Section 3.1, a server can offer two greetings to a new connection, 220 or 554.That's not what the section says. Rather, it says that two possible responses are 220 or 554. Nowhere does it say these are the only possibilities.
Well, OK, if there are other possibilities, their meaning, and indeed their very existence, could also stand some clarification.
And you're misssing the correct meaning (d), which is what RFC 5321 actually associates with the 554 code: (d) 554 No SMTP service here. Fail.
I think we can split hairs about whether it means "no SMTP service at all" vs. "no SMTP service for you", although it's easy enough to define so that it doesn't matter and the client does the same thing either way.
It follows, however, that the right thing for the client to do is bounce the mail. That's the entire point of having 554 as a possible connection repsonse.
That's a reasonable interpretation, but I would point out that it's sufficiently unclear that the guy who wrote the RFC has interpreted it differently.
Like I said, I don't much care which of the possibilities is the correct one, but we should document it.
Regards, John Levine, johnl at taugh.com, Taughannock Networks, Trumansburg NY "I dropped the toothpaste", said Tom, crestfallenly.
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