Spammers are always looking for new ways to target their message that will bypass (at least temporarily) standard spam tracking software. A recent target was Apple's iCal application through the use of iCalendar invites.
This attack upset many iCal users since declining the invite to delete the invite actually sent a notification to the spammer of the decline, validating the user's e-mail address for use in future attacks. Read more about this and a work-around here: http://www.cnbc.com/2016/11/25/chinese-spammers-target-apple-icalendar-users-with-sketchy-invites-for-black-friday-deals.html