I experience this problem in 2015 and posted the following description:
I will try the suggestion to populate a web page address in the contact made up-thread.
I use Outlook 2010 (on PC) and connect to the Outlook.com back-end (I have an @Hotmail.com email address) via the Outlook connector.
This works perfectly fine for synchronising mail message (and, I believe, Calendar entries). I have a single Outlook profile on my machine and just this one...