I have just noticed the same thing in my own Blogger feed and came here to look for answers as well. All the
outlook.com addresses were subscribed between June 2 and this week, and all seemed to have hispanic names or a combination of hispanic terms as a user name. I also deleted them one by one and I really don't relish having to do this every day. I wish there was a way to stop this, short of not letting people subscribe via email at all! Also, I wish there was a way to bulk delete them, as doing it one by one is time consuming since you have to verify the deletion every time. I had over 160 "subscribers" that had been added.