What about loops in the network?  If someone "beyond" PSUVM sends mail
to CEARN (for example) it is easily possible that the file would go
through the BITNET-EARNET link on the way to Europe but that a reply
would come back through DEARN-GWUVM instead.  If the networking software
were expecting all files from a node to come a certain direction, all
such loops would have to be eliminated and routing would have to stay
static.
 
If security is the primary concern, that is fine.  But for customers
with closed, secure circuits, the loss of flexibility might be bad news.
 
Playing the devil's advocate?
 
Nick