email - a flawed protocol?

[#1]

Take a look at IM2000 http://www.im2000.org/
It won't stop spam, but it will greatly reduce it and make it more traceable. In essense, the cost of storing mail is moved to the sender (or their nominated agent) because each outgoing message must be stored on a publically accessible server for later collection by the recipient.
Spammers will need to either compromise someones account so they can log into the outbound server using that persons cerdentials, or set up their own servers. Obviously, any servers used for spamming will get blacklisted making the latter a waste of effort - but unlike smtp, they can't spew out lots of messages before they get blacklisted because the message is only delivered when the recipient is ready to read it.
Other advantages include message tracking (know if it's been retrieved), reduced storage (only one outbound copy stored for multiple recipients), and only a small message 'header' need be passed through mailing list processors. The tracking ability means no need for 'bounce' messages - your mail program can tell you directly if your sent message hasn't been retrieved.
But as someone else has already pointed out, such a change is unlikely given the ubiquity of smtp 

[#2]

To someone's earlier point of having to grant people rights to send you mail, and how inconvenient a life like that may be:  From a personal point of view, I don't see that as a major problem or inconvenience, but more a mindset change.  I've already done the same or a similar thing for IM, facebook, linkedin, and a host of other community sites that have popped up over the last year or so.
I'm not saying it wasn't slightly frustrating but right now I know I'm not going to get MSN'd by someone I don't know.  Of course, even the newer communication methods aren't going to be future proof alone, it's just that email was the main means of electronic communication so had the most focus on it by spammers.
Not wanting to spark Linux/Windows wars, but I remember when people were saying Linux was better than Windows because you don't see viruses for Linux.  IMO that was merely because Linux's limited uptake at the time.  Now that Linux has gained its deserved ground, hackers and virus writers are targeting it nearly as much as Windows.
When uptake hits a critical mass, it also hits a critical threshold of vulnerability.
The more difficult I can make it for someone unknown to send me a message the better. 

[#3]

Quote from: SimonHobson

Take a look at IM2000 http://www.im2000.org/

This is something I read about a couple of years' ago, andI think it's a shame it hasn't gained greater traction.

[#4]

Dan, you've made me think, and it's kind of how I treat mail now and that is to think it's spam unless it meets the criteria of one of my rules. I've got lots of blackholing set up and run my own mail server but still get plenty of spam coming through but using rules to whitelist to stuff I know isn't spam means I know just need to do a quick scan for anything that wasn't picked up, fish it out and add it to the rules.