> Actually, they do. TCP/HTTP proxies used to be all the rage about 5 years
> ago, but now almost nobody uses them. And I worked as a network engineer
> in a telecom company (a while ago). Proxying breaks too much stuff for
> too little benefit and besides the limit right now is the air interface, > not the backbone networks.
The air interface also benefits from more compact traffic (see why Nokia or Opera set up their system, see why Google is working on SPDY now)> Besides: mail already works hop-to-hop.
>> I don't see the defenders of https purity complain smtps and imaps are
> Transparently doing smtps proxying would be.
No one legitimate would do https proxying transparently if there was another choice. People condemning transparent https proxying also refuse to give another choice (because that would be 'unsecure') even while the other choice works everyday with smtps (an smtp relay is just a mail proxy under another name)