You can check out the mx settings for the domain using one of the free online tools. If they have already sent you a message then you can look at the raw source of the email to see who and how it was sent.
I can forward all of them to a virtual personal assistant in Mumbai and have them deal with it all, just sending me a daily summary and maybe writing some auto-responses for me, and there'd be no need for me to disclose that fact to every person that writes me an email.
You can do the same thing with physical mail as well...there are services that can receive your mail, scan it, and send me stuff that seems relevant. No need for people to be able to figure out that you're doing that.
The fact is that I can contract that sort of thing out however I like. It's my mail once I receive it. I think it should be required for students to be protected when they have to use an email system when attending a school, so go ahead and get a firm statement from google on that, but the main part of this class action, the people sending email to people with gmail addresses, are barking up the wrong tree.
Except that people who are on regular GMail will probably use e-mail forwarding provided by their domain registrar. Especially since the free Google Apps for domains is gone.