Even an MTA should not see the IP address as an identity in
and of itself,
but it can use it to verify one of the identities Marshall pointed to.
Phillip and others who believe in cryptographic verification
will say that
there are other items to verify identity with. A digital
certificate isn't
an identity in and of itself but it can be used to verify
one's identity.
Passports, calling cards, birth certificates, social security
and social
insurance numbers[2], etc are not identities but are used to verify an
identity[1].
Actually an identity is simply a reference point for an accreditation.
The way the passport system works is that your name is in the
passport and there is a watch list of suspect persons that
is circulated to customs and immigration.
In this case there are two sets of accreditation going on,
positive (visas, issuers with visa-waiver privilege) and negative
(watch lists etc).
Many watch lists make no distinction between 'real names' and
pseudonyms. Does it make sense to consider 'Lenin' a pseudonym?
Phill