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Re: Per-session SMTP extensions (was: Re: 4yz Temporary Rejections is part of the SMTP Protocol)

2011-10-30 13:53:27
On 2011-10-30 09:41:42 -0400, John C Klensin wrote:
--On Sunday, October 30, 2011 11:10 +0100 "Peter J. Holzer"
<hjp-ietf-smtp(_at_)hjp(_dot_)at> wrote:
So, a new extension STRUCTUREDTEXT could be modelled after

220 server.example ESMTP server
EHLO client.example
250-server.example Hi client.example
250-SIZE 10000000
mail from:<me@client.example> SIZE=543210
250 2.1.0 Ok
rcpt to:<you@server.examle>
450 4.7.0 wait:55 greylisted

This doesn't allow the inclusion of structuredtext in the
greeting (or at least there is no way to alert the client to
its presence).


Keywords also need to be defined in (standards track?) rfcs and
registered to prevent conflicting use. So maybe a generic
STRUCTUREDTEXT extension isn't a good idea after all.

Worse, while one can work the odds, nothing prevents those
things you want to define as keywords from showing with
unstructured text following a 45x reply.

The replies are generated by the server. If the server supports
structured text it can make sure that it never generates a message which
can be mistaken for a keyword.

This should be possible even if the server includes error messages from
other software (spam filter, ldap, ...) in its messages. For example, if
the keyword:value pairs can only come between the extended status code
and the human readable text, it is sufficient to prefix any externally
generated message with a bit of explanatory text. Other ways of marking
the keyword:value pairs (e.g., enclosing them in []) may need more
complex escape mechanisms to avoid false positives.

So I don't think it is necessary that the client requests specific
information. It may be desirable, but right now I don't see a compelling
reason, and I lean towards keeping things simple.


   _  | Peter J. Holzer    | Web 2.0 könnte man also auch übersetzen als
|_|_) | Sysadmin WSR       | "Netz der kleinen Geister".
| |   | hjp(_at_)hjp(_dot_)at         | 
__/   | |  -- Oliver Cromm in desd

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