...

Now, even those people have shifted to a hierarchical architecture of instant-messaging servers.

In what way is IM hierarchial? Jabber/XMPP has a mesh-of-stars topology

That is hierarchy. One level is a star topology, the next level is a mesh.

which is the same as email's modulo some simplifications (mainly owing to the lack of forwarding).

In other words, it is not the same as email's. Of course it may end up that way but we can hope.

ISTR that you were arguing in favour of a chain-of-trust system for email back in November on the IETF list. I pointed out that the architecture you are proposing is essentially the same as inter-domain routing (IP & BGP) and Usenet, and you failed to explain how your ideas would solve the unwanted traffic problem for email given that the same architecture doesn't solve the unwanted traffic problem for IP or NNTP.

An abstract simplification of an architecture is not equal to the architecture itself. The fact that you can simplify different architectures into a similar abstract model, doesn't mean that they have the same problems. Problems often arise in the details of implementation, not in the theoretical models. I never claimed that my proposed email model would solve the unwanted mail problem. It was intended to carry authenticated sender info to the receiver, and to provide an authenticated reverse path for complaints to postmaster. And since it was based on negotiated bilateral email peering agreements, if the chain of trust was subverted at some point in the chain, the peer would have legal recourse to cut service. --Michael Dillon