c@one
    <-- b@one
    <-- a@one
  router = accept, transport = unset
c@one   [duplicate, would not be delivered]
    <-- b@one
  router = accept, transport = unset
b@two
    <-- a@two
  router = accept, transport = unset
c@two
    <-- b@two
  router = accept, transport = unset