Didn't Microsoft learn anything from Google? Wasn't there a huge brouhaha when it was found the google was reading all your emails to index them for searching? So now MS is going to do the same thing with Cortana... Good idea.
Yes, sort of. Keep in mind that Google wasn't just indexing for search. ALL emails are searchable by YOU as long as you have access to your email server. You can search through ISP-stored email via a third-party email client using POP3, for example. No, this was Google combing your emails to mine data. Including, but not limited to, mining for advertisement purposes. As in, hey, here's an email where he talks about buying a new car. Boom lots of targeted ads about buying new cars headed to a banner ad near you, just as an obvious example of one thing they did with your data.
Plus, you can turn off Cortana. You couldn't do too much about Google searching your emails at the time they got caught with their hand in the cookie jar. They may have added more control later, I don't know - I don't use MS or Google email and I didn't follow up on the story. But at least initially you weren't given a choice.