Anyone using Office365 or using Exchange Online Protection (EOP) are about to see a change in how bulk mail is handled. Microsoft consider bulk mail to be a category in between spam mail and good mail and have started assigning a Bulk Complaint Level (BCL). This level is determined by EOP based on the mails compliance with good sending practices and customer feedback. Like with Spam Mail, administrators will be able to configure a threshold where action against the bulk mail can be taken. In the case of bulk mail, the action will be to treat it as spam. For more details see the article at http://blogs.office.com/2014/11/24/block-spam-holiday-season-new-enhanced-bulk-mail-experience-eop/