Fixing Outlook 2016 “Either there is no default mail client…”

I have a client who can’t open .MSG files with a brand-new Office 10 Pro system, and gets the following error when he tries (using Outlook 2016, installed from Office 365):

Either there is no default mail client or the current mail client cannot fulfill the messaging request.

You might think “aha, I just need to go into the control panel and fix either file associations with .msg files, or perhaps MAPI settings.” You would be wrong. Nope, you’re gonna have to delete a registry key, because of course you are. You’re using Windows!

Open this registry address in regedit:


And delete the key with Data value of “Microsoft Windows MAPI Preview Handler”.

Poof. That’s it. No more errors, stuff opens as it should. Yay.