Hear my story:
I signed up to sbc yahoo! dsl and I got a bounce of free email accounts @sbcglobal.net with 100M inbox.
I thought: nice!
After a week or two, I get an email from sbc/yahoo! with the subject "introducing your bulk mail folder".
The email explained how to take advantage of it. So I thought:"uhm..nice, even if I didn't give away this address to any website yet..it may come in hand in the future"
The day after I got around 70 spam mails in my "new" bulk mail folder.
MORAL: SBC/Yahoo! sold my email address to some damned mailing list. Since then I get a lot of spam....and I pay for that account!!! (it's included in the DSL service).
