[Asrg] where the message originated (was: DKIM role?) (SM)

[Ian Eiloart]

--On 20 January 2009 20:01:59 +0100 "Peter J. Holzer" <hjp-asrg at hjp.at> 
wrote:

>
> There are, if we are only interested acception/rejection of the message.
> You cannot include specific messages, of course (currently I just
> concatenate all the rejection reasons into a single message).
>
>
> The real problem is in the phrase "this particular message". At the time
> the server receives the first "RCPT TO:" command it has no way to
> know that this is a new delivery attempt for a message which was
> temporarily rejected earlier, much less which message (envid is
> per-transaction, and you couldn't rely on the client sending it anyway).
> So, as a weak approximation, I use sender/recipient pairs instead of
> message/recipient pairs as elements of the sets. This works quite well
> because a recipient usually wants to receive all messages from a
> specific sender or none. But yes, theoretically it can happen that the
> sets are split again and again until each recipient is in a set of their
> own. In practice I haven't seen it yet (after more than 3 years, but
> admittedly on a relatively small number of email addresses).
>
> 	hp

Oh, that's a pretty good solution. There are edge cases, and perhaps even 
exploits, but it's probably going to work most of the time - provided the 
client MTA ignores 4.2.5 of the RFC. It still delays messages for some 
recipients, but only up to an hour or so. It might cause problems with 
conversations on lists like this - but they could be mitigated by caching 
the "sender/recipient/source IP" triplet.

The exploit, of course, is that spammers could open channels by sending 
apparently innocent messages.


-- 
Ian Eiloart
IT Services, University of Sussex
x3148