User blog comment:DaNASCAT/Technical Update:September 24, 2013/@comment-460966-20130925121118/@comment-954127-20130925222732

Yeah, had it too. It turns out that something most likely related to the weekly updated checked marked "...someone joins" and "...someone edits" at all the wikis you are a admin at. Happened around 5 am central time. Anyways best thing to do is uncheck mark those on Preferences>Email.