Apparently, for every $1 invested the return is a whopping $44.25 :) However, though, I have my doubts. In fact, I know marketing (of any type) to be more like a poker machine were a large bankroll and some skill is needed to win.
OK, here is another stat about email marketing:
Of all the email sent by companies, 82 percent is opened! That's amazing. Myself, I rarely open emails sent, but I'm not an email guy.