The general idea is that each time a subscriber gets sent an email, the message doesn't get delivered into the main in box until the sender responds to an Earthlink-sent confirmation message. That message may have a graphic of a number that the original sender needs to type into a message to the confirmation engine. Only after that confirmation is received will the message become blessed by the system and delivered.
Of course this is a big hassle for people sending messages, but not as much as one might think. Email today is already fraught with the danger of messages getting caught up in over-zealous spam filters, or - even more commonly - mistakenly ignored by recipients who don't understand the subject message. Going through this confirmation process will take an extra minute, but at least it better guarantees the content will get read.
This brings up an interesting point about the economics of email marketing. Where email is easy to abuse by sending out mass spams, communicating with users of this sort of system requires a human labor element that raises the cost of the medium to the point that it requires some intelligent targeting. In other words, by making email marketing more expensive, the quality of it should be raised in direct proportion.
Instead of dumping marketing messages to gross lists of email addresses, email marketing in this new environment would become much more like that envisioned a decade ago as "one-to-one" marketing. In fact, once a human is involved to get past the gatekeeper, it might prove only nominally more expensive to have those humans actually interact with the customer.
Email marketing might become a lot more like today's telemarketing. Before you squinch up your nose at that remark, just remember that even in the worst of days, you only get a few telemarketing calls, and those on email can be easily ignored.
This may indeed defeat spam, but non-intuitively, it may also save email marketing from the clutches of klutzy spammers.