Hi Ken
My name is Andre Da Costa; an Independent Consultant, Windows Insider MVP and Windows & Devices for IT MVP. I'm here to help you with your problem.
Eudora is not officially supported or actively developed to support Windows 10.
You could try launching it in compatibility mode:
Run Old Software on Windows 10 with Compatibility Mode - groovyPost
https://www.groovypost.com/howto/run-old-softwa...
Ultimately, your best option if that does not work is to rollback to your previous version of Windows 10 and stick with it if you need to use Eudora:
Open Start > Settings > Update & security > Recovery > under Go back to my previous version of Windows 10, click Get started.
or
Press Control + Alt + Delete
Click Sign out
At the Sign In screen, hold down the shift key on your keyboard while clicking the Power button on the screen
Continue to hold down the shift key while clicking Restart
Continue to hold down the shift key until the Advanced Recovery Options menu appears
Click Troubleshoot
Click Advanced options
Click Go back to the previous version of Windows
Windows Update might attempt to upgrade to Windows 10 1809 again. See instructions how to block it:
https://www.groovypost.com/howto/block-windows-...
Eudora website for support:
https://www.computerhistory.org/atchm/the-eudor...
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.