-----Original Message-----
From: owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org
[mailto:owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of SM
Sent: Thursday, October 27, 2011 6:36 PM
To: Hector Santos
Cc: ietf-smtp(_at_)imc(_dot_)org
Subject: Re: 4yz Temporary Rejections is part of the SMTP Protocol
From RFC 5321:
"Unfortunately, variations, creative interpretations, and outright
violations of Internet mail protocols do occur; some would suggest
that they occur quite frequently."
That's a pretty strong argument in favour of creating something new rather than
overloading something old. But that too runs headlong into likely
interoperability concerns. There's a bit of induced paralysis there that needs
to be overcome.
Someone else suggested nothing parses SMTP replies beyond the three digits.
That's not true in ESMTP; the enhanced status codes (if used) and the reply to
EHLO itself are structured. It's not true in pure SMTP either, where I think
some of the replies are specified beyond the three digits (the 220 greeting,
the reply to HELO, and the 221 message, as I recall).
John suggested a new reply code series, but that scares me a bit; what would a
staunch legacy implementation be likely to do with that?
-MSK