The problem with this so-called solution is that any computer that gets hacked can have authentic email sent from the source so any botnet with lots of hacked PCs and servers can send authentic spam, just like they do now, big whoop, NEXT!
The only way you'll ever stop phishing, or spam in general for that matter, is to educate the idiots.
Anyone willing to buy pharmaceuticals from unsolicited spam, stuff that could be potentially deadly, and stuff it in their stupid mouths, obviously needs some education instead of more technology.
Fixing email alone doesn't stop phishing as it can be done via twitter, hacked domains, hacked ad servers, any number of methods including the cold calling on the telephone.
Stop wasting money on screwing up email protocols and spend it on good old PSA on TV, radio, email, start shoving the message in their faces and maybe they'll listen.
I'm thinking people that fall prey to phishing and spam should be required by law to take an anti-phishing class, kind of like traffic school for bad drivers, before they'll correct the financial loss the phishers caused the victim. I know that sounds a little silly but the victim wouldn't be a victim if they were better educated and more diligent about simple things like the URLs the phishers took them to visit.
Legislate a shrink-wrap test pre-installed on all new computers. The computer won't activate unless you can pass a computer literacy test that's built into the box which includes a section on phishing and spam. Then require a similar computer literacy test by all ISPs before activating any online access. Once again, when you sign up for an email account, beat the consumer over the head with another test about spam and phishing before being allowed to use that email account. Just to be safe, make everyone currently signed up for existing emails take the test to continue using those accounts. Eventually, people will get the idea they might not be annoyed with all these annoying online computer literacy tests if they pay attention and stop falling for phishing and spamming emails!
I'm thinking about every 6 months people should be reminded how to avoid phishing and be re-tested to continue using those accounts.
Stop the stupidity and you stop the spam when it's no longer profitable.
Unfortunately, greedy idiots will still think someone from Nigeria is really going to give them millions or those cheap ED pills from the Avian Guano Island Republic are perfectly safe.
Wait, they've tried educating people about those deadly cigarettes too, never mind.
Excuse me Sir, may I have another cup of technology please?