Right after I posted, I found the answer and am posting it here for anybody who has the same issue.
My system is Windows 10 and I have been trying to get rid of Outlook simply because it is just plain awful. I have tried a few different email clients but could never get my LL20 to open up the new email client… it would always open up Outlook.
Here is the solution:
When you change the Windows default email client, it makes a change to the following registry key:
HKEY_LOCAL_MACHINE\Software\Clients\Mail::(default) registry value
where it names the default client
BUT it doesn’t change this key:
HKEY_LOCAL_MACHINE\Software\WOW6432Node\Clients\Mail::(default) registry value
When I manually change it, then LL20 (which is running in my 16 bit program) then connects to my correct email Client.