Re: rough sketch of a potential solution

> > > > * Secure e-mail.  What should MUAs display as the sender
> > > > address?  The
> > > >   ASCII version or non-ASCII, looked up via the service you
> > > >   propose?
> > >
> > >They should show the address in the sender's certificate as the
> > >party who signed the message, which shouldn't have to be the same
> > >as the From address anyway.  The addresses in the message header
> > >should be displayed separately.
> 
> Actually, that's not a very good idea.   I would say that the address
> (or one of the addresses if we want to syntactically correct) MUST
> match the address held in the signing certificate or you lose much of
> the benefit of digital signature wrt to recipient trust.  

Well, we've already got the capability for multiple From addresses, and
now we'll have a situation where each of those From addresses can have
multiple representations.  So we inherently have a situation where the
parties who sign a message may not match the list of addresses in the 
From field.  The only question is how the recipient's MUA should
represent this situation to the recipient.   It can say "message is
signed but the signature doesn't match the From addresses" (which is
misleading), or it can say "signature invalid" (which is worse),
or it can say "message is signed by [email protected]".

But now I remember another one of the reasons for allowing the mapping
service to sign address mappings (and to include those signatures in
the address mapping header extensions) - it was so that if a message were
signed by [email protected] but shown to the recipient as if it were from
[email protected], it would be possible for the recipient's MUA to verify
that the two addresses really were equivalent.