The Problem with Spam
It must also be noted that more and more email marketers are struggling with spam filters, which are designed to protect email users from unscrupulous and unsolicited advertising. The problem arises when spam filters do such a good job that they succeed in filtering out legitimate marketing messages that email recipients have requested to receive.
Unfortunately, as spam proliferates, as it undoubtedly will, the filters will only become better, causing email marketers to scramble to devise new ways to get their messages out to the public.