If clicking on a mailto link brings up a Google webpage, you clicked "yes" when chrome browser asked you whether you wanted to launch Gmail when you click on a mailto link.

If Outlook does not open, follow this Win 8 guide to quickly fix: 

  1. Open Control Panel > Default Programs, Associate a file type or protocol with a program:

  2. Sort 'Current Default' column and find MAILTO

  3. Click 'Change program...' and select Outlook:

Now Outlook will open mailto links as it used to before installing Chrome browser.