RE: [Asrg] TitanKey and "white lies"... (Faking SMTP hard errors "improves" C/R utility?)

[Vernon Schryver <[e-mail]>]

> From: Yakov Shafranovich <[e-mail]>

> ...
> >a) I am a sender with a CRI system and send a message to a recipient with a
> >CRI system.  My CRI system remembers I sent a message to a particular
> >recipient.
> >b) The recipient receives my message and holds it.  The recipient sends me a
> >challange message with CRI headers.
>
> If we were using some form of SMTP-model, then the recipient would not 
> actually accept the message. Instead his system would issue some form of 
> SMTP error code back, something like "450 Need to verify sender". This will 
> force the sender's system to hold on to the message until the C/R process 
> runs its gamut.
> ...

SMTP clients that merely follow RFC 2821 without knowledge of your
CRI system will retry the message on their normal schedule.
See section 4.5.4.1 of RFC 2821.

You are surely not assuming that all SMTP clients in the Internet will
be replaced before you turn on your CRI system.  So you must be assuming
that SMTP servers can recognize retransmissions of the same message
or same sender and not challenge a second time.  Have you considered
the practical difficulties of that?


By the way, how do you handle MX secondaries?  What if the SMTP client
happens to choose different MX servers for its attempts to send the
message?  How do you avoid sending a challenge from each MX server,
in practice and not merely theory?


Vernon Schryver    [e-mail]
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