Eric Thomas of SEARN writes, on this topic, that it is impossible to control
the anonymous postings from the anonymous alias servers.  Again, there is a
confusion between policy and implementation.  If (and this is if) an agreement
were reached on policy that said anonymous postings were not allowed in
some form, then the question of preventing would come up.
 
For preventing or constraining anonymou alias servers:  I don't see this
becoming a difficulty at some point in the future, for I do not believe that
the present relatively anarchic network-connection mode will exist for more
than a few more years.  The network will become institutionalized and
regulated, and connections to the net will be subject to  rules and sanctions
which if not followed will result in disconnection or other legal or
quasi-legal action.  This is all hypothetical, though; tthe point remains:
what do we want?
 
--Peter Graham, Rutgers University Libraries