I get these types of emails daily -- never bothered to check whether they are YC or not as I don't read them; I can tell from the first sentence that it's not a company I know and am doing biz with and it goes directly into z-file. Most seem to have gotten my email address from LinkedIn, others from GH.

Side note but the trick I learned, at least with gMail is not to delete the email (which doesn't prevent you from getting new ones), or even reporting as spam (which may or may not work), but instead dragging it into the Promotions tab, into which all future emails from that email address will automatically go. Promotions tab then acts as your Trash.

The quickest way to get me to never do business with you is to send me spam.