Microsoft Outlook

Abandon Outlook and use a web based email program.

I quit trying to use Outlook because it was too problematic and I discovered I could set up my Hotmail account as my email client so now whenever I click on email it goes strait to my Hotmail.

If you can prove this and the person has no legitimate right of access to your mail, call the police.

That is invasion of privacy, but you will need to be able to prove it.

It might get him/you fired, due to the law of unintended consequences coming to life...

Check your rules, this person could have had accessed your outlook and created a rule to send a copy of your email to him/her.

Set up another e-mail account using hotmail or G-mail (or both) ,and then send yourself e-mails full of misinformation that will make this person make a fool of themselves. Take a little time and exploit their weaknesses. Get in their head, and then crash the car.