Re: [Asrg] pre-rfc thought balloon: ESMTP DATAFIRST

[der Mouse <mouse at Rodents.Montreal.QC.CA>]

>> A new ESMTP extension DATA-CALLBACK.

>> The current DATA phase becomes a the header only portion of the
>> message.  A new header also provides a token used by the MUA to
>> retrieve the rest of the data.

I like this, for normal mail transport.  I don't see it as being of any
particular anti-spam use, though; spam will simply be sent without
using it, the way it is today.  (Given all the usual deployment issues,
it'll be a long time before anyone but the most lunatic fringe can
afford to reject mail not sent using it.)

> A suggestion has been made before (here I think defintely elsewhere)
> that a temporary error response might be issued after RCPT (indeed
> after any command) and before DATA which would allow the recipient
> MTA to carry out asynchronous verification of the sender MTA and any
> other checks deemed necessary without the cost of recieveing the
> message content.

Except for the bit about putting a minimum delay on the retry, this
amounts to greylisting.  The hardest part here is telling whether a new
SMTP session is a retry of a previously-rejected one or a new message.

/~\ The ASCII				der Mouse
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