In our experience, there's a few ways to figure out whether or not it is a genuine email of interests. Since there are rules regarding contact, it can be hard to distinguish but there's subtle hints.
Feel free to add on...
1. If your kid's name isn't on it, everyone got it.
2. If you scroll down to the bottom of the email and can press "unsubscribe from mailing list", everyone got it (even if your kid's name is on it).
3. If it sounds like a sales-pitch more than an interest letter, everyone got it.
With number 3, sometimes it is hard to tell whether or not it's genuine interest. However, coaches will sometimes add a "we saw you play (and would like you to attend our camp)" or a "you played very well this weekend (and would like you to attend our camp)". Catch my drift? They'll personalize it just enough to be able to tell it apart from the generic email-blast if they really want to see your kid and get them on campus at their camp so they can truly talk to them.
Their emails can be found through the league they're in, recruiting profiles (NCSA, TDS, etc.), your club coaches, etc. Information travels further than you'd think in the soccer world.