21.6 Mail Box Model

In the mail box model, each agent is equipped with his own mail box. In the simplest case, the agent is known to others only through its mailbox. A mailbox can be simply be modelled by a port and an agent by a thread reading the stream of this port.

declare 
MailBox  % will be bound to a port
proc {MakeAgent Process MailBox}
   thread {ForAll {Port.new $ MailBox} Process} end  
end 
proc{Process X}
   {Browse 'new mail arrived'}
end 
{MakeAgent Process MailBox}
{Port.send MailBox 1}
{Port.send MailBox 2}

Do you know how should a newgroup model work?