The way modern spam filtering works, particularly through the likes of Gmail, is that once you are flagged as a spam risk, it will be increasingly difficult to get subsequent messages to arrive in inboxes instead of spam folders. If you open up a new Gmail account and the first thing you do is send a bulk communication to 500 recipients, it is almost guaranteed that Google will step in and block your account. The best way of keeping on the right side of spam filters is to send email to people who will be interested in what you have to say.