Thunderbird is set as the default email client, and clicking "mailto" links on web pages and in Word aor PDF documents works just the way it should.

However, the right-click context menu "Send to > email recipient" insists on using Outlook. I've seen a number of threads on this topic, but no definitive solution. This used to be so simple back in Windows 7, but Microsoft seems to have made it much more difficult -- or impossible -- to properly configure this setting.