is it just me or not ? Even if this is not yet implemented, I am stuned that nobody ask this in this forum (or I did not well searched). Windows does not see Evolution as a registered mail client and you cannot set as default one. Each program that tries to open a new mail does not use evolution.
I tried to search myself how to tweak registry, but not being an expert, I only succeeded for mailto links in web pages. What seems missing is a DLL for Mapi. Details on what I tried at the bottom of this page :