I use WPO and Outlook, and they've never played well together. I've just upgraded my MSO to 2016, so I thought I'd have a new look..
I was surprised to see that I was not only offered the option of using my Outlook 2016, but that it opened, and I was able to see my "Contacts" list. It only showed the entries with e-mail entries - but that's an old issue and an e-mail entry in Outlook of email@example.com fixes that. However after that it became a bit more difficult. If I searched for "Colin" it inserted the first "Colin" in the document.
If I went to "Envelope" and selected "Colin" I saw the list of "Colin"s,and when I selected the one I wanted using an old custom format, it displayed correctly. However, when I the clicked on "insert" it inserted a different format, starting with the "display name" (which includes the e-mail). When I tried to create a new custom format things became very odd. To get the address to display I had to select [Zip/Postal Code]; to get the Zip to display I had to use [Street].
Twice whilst exploring this area WPOX8 crashed.
Has anyone else explored this?