Bulk E-Mail Marketing

Perhaps it is me and that I do not understand how internet marketing works but I was looking at a list of keywords put out by Facts About Adsense and the number one keyword that has the highest average bid price is bulk email marketing. I can understand how dating, web design and hosting and insurance can all be at the top five but how can bulk email marketing be on average the highest bid for keyword? I think of bulk email marketing and I think of spam and the definition by most law enforcing entities is something along the lines of unsolicited bulk email. Perhaps the people involved in bulk email marketing consider their email to be solicited and wanted such that the recipient has subscribed to the bulk email being sent. I say the hell with bulk email. I would like to further clarify the definition of spam if not already done as if it is not personalized for me and that the E-Mail address is not a valid E-Mail, for example if I cannot reply to the person. The amount of mail I get that cannot be returned is quite annoying. I like to return spam to the user, thanking them kindly of course. Although using spam and bulk E-Mailings does have its benefits in intermediate and advanced foreign language classes. I have done this in my English classes in China.