"It was an advertisment! 4th class mail "

4th class mail is generally know as junk mail. People love to hate junk mail and there are whole sites dedicated to ridiculing bad junk mail. The volume of junk mail hasĀ  been a hinderance to postal services, to obtain a 'bulk mail' permit in the United States the mail must adhere to certain specification to make it easier for the sorters and carriers. Something I'm sure Bukowski would have approved of.