Google will not ban you for sending out mass emails. But gmail, hotmail, yahoo, etc may marked you domain/server as 'spam' and you'll not be able to send out any legitimate emails then. And if you sure that you're not sending out spam, then you're fine for sending out 500,000 email list - just spread the sending process over a week or something. Make sure you can give a good answer to your hosting if they thing you're sending out spams though.