Twenty percent of legitimate email never reaches the inbox. Blame the ISPs' ongoing fight against spam-and then, look in the mirror. Today, your sending practices play the major role in determining whether or not your email makes it to the inbox. The crude, content-based tools that ISPs used to counter the "spam crisis" are no longer the main factor in determining whose mail gets through. ISP relationships aren't that important any more, either. It's your sending reputation that drives deliverability, and your reputation is all about your numbers.