Thanks, Ronel, for prompting me to revisit this problem, which I've ignored since my original report.
In the interim, I've upgraded to Fusion 5 and installed numerous Windows 7 updates.
When I found no trace of WIndows Live Essentials, I downloaded the latest released and installed just the Mail component. I encountered an account authentication speed bump. After that, initial tests shows Mail is working OK.
But I'm sticking with Thunderbird as my default email app on Windows 7.
-- Ward