The POP->IMAP example is excellent, since it really demonstrates my point. IMAP is rather popular in some local area network environments. However it's long history has failed utterly to seriously displace POP on a global scale.
Exactly right. The benefits of IMAP are obvious to everyone who has looked at it in any depth, and yet it is very thinly deployed. The main reason: the perceived additional administrative overhead.
EAH> Large-scale mail carriers would probably switch quickly if EAH> the accountability feature proved useful,
and now we are back to hypothesizing about the behaviors of mega-corporations with massive installed bases and a rather poor history of adopting changes from the IETF community.
So far on this thread, we have heard from none of the "large-scale mail carriers", although we have heard that the spam problem is costing them millions of dollars a year. That should be a clue to the IETF list. If there is a problem that is affecting a company to the tune of millions of dollars a year, and that company thinks that the problem could be solved, they would spend that much money to solve it. Please note that they aren't.
I have spoken to some of these heavily-affected companies (instead of just hypothesizing about them). Their answers were all the same: they don't believe the problem is solvable for the amount of money that they are losing. They would love to solve the spam problem: not only would doing so save them money, it would get them new income. Some estimate this potential income to be hundreds of millions of dollars a year, much more than they are losing on spam. But they believe that the overhead of the needed trust system, and the cost of losing mail that didn't go through the trust system, is simply too high.
You might disagree with them, and based on that disagreement you might write a protocol. But don't do so saying "the big carriers will want this" without much more concrete evidence as to their desires.
--Paul Hoffman, Director --Internet Mail Consortium