Re: SMTP RFC: "MUST NOT" change or delete Received header

[Phillip Hallam-Baker <[e-mail]>]

On Sat, Mar 29, 2014 at 10:59 AM, John Levine <[e-mail]> wrote:

> >What do people today think of the SMTP RFC's current requirement that
> >mail programs and servers must not under any circumstances change or
> >delete Received: headers? Is exposing sender IP addresses to any
> >attacker who can view e-mail headers, for the purposes of preserving
> >trace information, really worth it when weighed against considerations
> >like security and privacy?
>
> The headers are useful for debugging, particularly for things like
> forwarding loops.


Debugging is not a justification for MUST.

Never, ever, ever. The justifications are

* Interoperability
* Security / stability.

The justification for MUST was I suspect to prevent infinite recursion mail
loops. For that particular purpose a count is sufficient.



> Particularly on public webmail systems, it lets you
> see where spam is coming from, and offers the possibility of alerting
> the originating operator if you think they'll care.  Gmail is notable
> in redacting this from some (not all) of their outgoing mail.
>
> What sorts of attacks do you think are enabled by allowing mail
> recipients to see the headers?
>

The requirement does not meet contemporary requirements for MUST so it is
invalid. Systems out on the net are justifiably ignoring it.


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