You've done all the necessary work to try to build a legitimate spam-free email list. You adhered to all of the appropriate white hat marketing tactics; you've optimized your site for search engines, used pay-per-clicks and offered a free incentive such as an e-book or newsletter to draw subscribers into your list. Yet, when it comes time to actually email your potential subscribers, you get an unpleasant surprise... dozens maybe even hundreds of returned emails. You wonder what you did wrong because you know for a fact that all of your emails were opt-in. So, what's the problem? The answer to this question is simple: your web hosting provider.