Re: [art] Alissa Cooper's No Objection on draft-ietf-appsawg-mdn-3798bis-15: (with COMMENT)

[Barry Leiba <[e-mail]>]

> = Section 6.2 =
>
> "Disposition mode (Section 3.2.6.1) can leak information about
>    recipient's MUA configuration, in particular whether MDNs are
>    acknowledged manually or automatically.  If this is a concern, MUAs
>    can return "manual-action/MDN-sent-manually" disposition mode in
>    generated MDNs."
>
> I see why this is here, but doesn't recommending falsifying these fields
> put their integrity in question whenever they are set to manual? I mean,
> why would recipients trust this information if the RFC actually suggests
> sending a field that lies about an MDN being automatically acknowledged?

This comes from my pushing on the point, and is the only reasonable
mediation we could come up with.  Here's the summary of the
discussion:

- I don't see any use in having this field at all.  There's nothing
useful the MDN recipient's mail system can do with it, and it only
serves to expose information about the MDN sender's configuration
unnecessarily.  I'd rather see it removed entirely.

- That said, it's been required from the beginning, so (1) all
existing implementations send it, (2) existing implementations expect
to receive it, and are likely to consider the MDN invalid if it's not
present, and (3) implementations are not expected to be reworked to
match this spec if we should change that now.

- Because of (2) above, we can't just recommend not sending it.
Further, the field wasn't designed to be extensible, so we can't use
some value such as "unknown" -- that would most likely have the same
effect as in (2), that implementations would consider those to be
invalid MDNs.

- The only thing that leaves is recommending a "standard" value to
send if you don't want to expose the real information.  That value has
to be one of the two defined values, and "manual" is the less bad
option (as opposed to telling the recipient's system that you're
configured to automatically send MDNs).

- And because of the first bullet above (that there's nothing useful
to be done with this information anyway), lying about it doesn't hurt
anything.

It's a bad, but usable solution to an unfortunate problem.

Barry