Dina points to "email is dead" in reference to teens by Danah Boyd
"Now, let's talk about youth. They have email accounts. They get homework assignments sent there. Xanga tells them that their friends have updated their pages. Attachments (a.k.a. digital Netflix/Amazon packages) get sent there. Companies try to spam them there (a.k.a. junk mail). Sifting through the crap, they might get a neat penpal letter or a friend might have sent them something to read but, by and large, there's not a lot of emotional investment over email.
That said, take away their AIM or MySpace or SMS or whatever their primary form of asynchronous messaging with their friends is and they will start twitching and moan about how you've ruined their life. And you have. Because you've taken away their access to their friends, their access to the thing that matters most to them. It's like me taking away your access to blogs and email and being forced to stay at the office just because you showed up late for work.
There is a difference that I see in the way IM and emails work. On an IM, you get messages from a set of accepted people - who talk about stuff that (mostly) matters to you. On the other hand, your email account is a dropbox for a bunch of uninteresting stuff - mostly spam. However, if you think about it, email has its advantage too - it can be archived, encrypted, signed, personalized, sent across networks (i.e. your gmail.com account can send an email to yahoo.com email id, but you cannot chat with your yahoo! messenger friends from gtalk.
Maybe something equivalent to your IM-buddy list can be done for emails too. You have an email account and that accepts emails only from a whitelisted set of email-ids. Whenever you get an email from a new id, you can either add him to the buddy list or you can report the message as a spam and block the email id. Next step would be to integrate the notifications of new messages into you own desktop and an online presence indicator.
Just some food for thought 
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