Re: [apps-discuss] Comments on Malformed Message BCP draft

Tony Finch <dot@dotat.at> Mon, 18 April 2011 19:13 UTC

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Date: Mon, 18 Apr 2011 20:13:32 +0100
From: Tony Finch <dot@dotat.at>
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Cc: ietf-822 <ietf-822@imc.org>, General discussion of application-layer protocols <apps-discuss@ietf.org>
Subject: Re: [apps-discuss] Comments on Malformed Message BCP draft
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ned+ietf-822@mrochek.com <ned+ietf-822@mrochek.com> wrote:
>
> And it isn't a binary choice between rejection and fixup either. What sort of
> fixup makes sense can change over time.

The draft suggests an intermediate option, which is to process the message
using a grammar with more lenient handling of error cases but to pass on
the message unchanged (if it gets passed on). A lot of the risk comes
from doing this (or rather, from doing this inconsistently). I think I'd
like to make a distinction between a relay (which is transparent) and a
security gateway (which does fixups). They should have consistent
behaviour, by which I mean that if a transparent relay is presented with a
corrupt message, it should treat it in the same way as a standard parser
would treat the same message after it has been fixed up by a security
gateway.

Whether a message gets rejected or not is a somewhat different matter. I
think submission servers can and should be a lot stricter than an MX can
be. Either way, every system needs to parse borderline cases more
consistently.

Tony.
-- 
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