[Asrg] On assertions

[der Mouse]

> A self-assertion which has a positive effect on the delivery rate of
> the apparent sender is unlikely to be believed, as any crook can make
> that assertion, and many will.

It's not quite so clear to me.

A self-assertion on the part of a sender which if believed would have
positive effect on mail _apparently_ from that sender, well, mostly
agreed, but see below.

A self-assertion on the part of a sender which if believed would have
positive effect on mail _actually_ from that sender seems like a
clear-cut case, but it's not quite so simple.  Such assertions are
unlikely to be accepted blindly, but they _can_ be of use in that they
inherit the claimer's reputation: a sender with a good reputation can
usefully make such claims.

> A self-assertion which has a negative effect on the delivery rate of
> the apparent sender of mail is likely to be believed, as there's no
> real incentive for the domain owner to publish it, apart from
> "because it's true". "I send no mail" is the obvious example of that.

I disagree that there's no incentive to apparent senders to publish
such assertions: it makes them less attractive forgery targets.  If the
entity has a good reputation in non-email respects, this may be a
substantial benefit.

> "I send no mail" is interesting in another way, as it (by definition)
> needs to be transmitted out of band,

I disagree that it _by definition_ needs to be out-of-band; it could be
sent in-band perfectly well - it's prima facie false in that case, but
that's not the same thing.  (Admittedly, this is hairsplitting.)

> Many other assertions are transmitted in-band "This is a mime
> message", "This was sent on this date", "this was sent by this
> person", "this is an html message" and so on.

Interesting you mention "this was sent by this person", because that's
an example of a self-assertion that can improve delivery - many
recipients use per-apparent-sender whitelists.  The major reason such
assertions aren't useless in practice, I think, is that the assertion's
effect is recipient-dependent.

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