I think liberal use of specialized aliases and temporary mail ids would help. Rather than trying to impose filtering, assure that mail addresses likely to be harvested by spammers will bounce.
I’m not using a temporary mail address service, but I use a forwarder at pobox.com as my published email address. They allow me to administer three aliases pointing to my “real” address, and there’s one of them I change every month or so. The current value of that one is what I use for online shopping, or registration with sites that I don’t wish to maintain a permanent relationship with. If I did that more often, an actually temporary address service would be useful. You get the immediate responses you need from the interaction, but when a spammer (or the online retailer who now has a “business relationship” with you) tries it a month later it bounces.
I have a credit card with virtual numbers which I also love. When you hand out a virtual number, not only does it have an expiration interval, but the issuer will only accept charges from the first party that uses the number - ie, the merchant you wished to be allowed to charge on the number. I really like the idea that “flybynight.com” doesn’t get a credit card number that anybody who cracks their DB can actually use, nor will flybynight be able to use it shortly after my transaction with them completes.
I think a mail alias along these lines would be useful as well. A server can hand you a new alias, which you hand out to somebody you are willing to correspond with. The server notes the first incoming email addressed to that alias, and restricts it only to that party. A spammer who gets ahold of that address is unlikely to want to try to figure out who they have to masquerade as to use that address, even if the information was obtainable from the context their harvesting program retained.
It goes without saying that a server which hands you temporary or one-shot aliases also allows you to cancel them manually.
In effect, I think there’s a real need on the internet for a cohesive “one shot” identity, suitable user tools to create them easily, and support on commercial sites to play ball with the idea. That, plus realization by social, blog and messaging sites that they should provide “reply to” mechanisms for their members that don’t expose an email address, or realize that the email address they should use to communicate with you about your account may be different than the one that should be publically displayed to other users and susceptible to harvest. For instance, I could still allow email here by entering one of my “one shot aliases” into my profile. In the infrequent instances that another member sends me mail, I will get it, and that member will continue to be able to send me mail as long as they send it from the same address (or, I may reply to them, and give them my “real” email). I will then enter another one-shot into my profile. A spammer that figures out how to harvest this board will get through once, and then bounced in the future.
People are already doing variants of this informally by using “throwaway” hotmail type accounts when the do something that they think is likely to put them on a spammer’s list. I would like to see actual support for it on mail servers, with enough of a standard for the request that your mail client and browser plugins could provide you a “create alias” interaction. You park on the “email” field on your online shopping site, select “create alias -> temporary”, and “dogwood357@myserver.com” or something like this gets filled in and created as an alias on the mail server. A month later the mail server removes it again, and the vendor you had the interaction with can’t send you annoying notices about their sales.