Re: Per-session SMTP extensions (was: Re: 4yz Temporary Rejections is pa

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
> > ENHANCEDSTATUSCODES:
> >
> > 220 server.example ESMTP server
> > EHLO client.example
> > 250-server.example Hi client.example
> > 250-SIZE 10000000
> > 250-ENHANCEDSTATUSCODES
> > 250 STRUCTUREDTEXT
> > 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).
> Right
>
> > 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.

        hp

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| |   | hjp(_at_)hjp(_dot_)at         | 
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