Eek, I hope not. That would make me and anyone else who's ever written a form-mailer or similar with "[email protected]" or "From: [email protected]" guilty of wire fraud.
> And any email provider should obviously immediately blacklist them. Worse than spam.
I'm a mail provider. I'd like to, but the reality is that a lot of people are on LinkedIn on purpose, and it would be wrong for me to blackhole them just because I don't like them. Fortunately, anybody on my mail system that doesn't like LinkedIn can easily adjust their own SpamAssassin settings right from the webmail interface.
This wouldn't be terribly different from (not that I know an example) me sending a letter to friend A and putting friend B as the return address, sending a letter by proxy. Of course in that case, there isn't even a method to see who actually sent the letter, whereas the information on who sent the email is still contained in the email.
And any email provider should obviously immediately blacklist them. Worse than spam.