This question was asked and answered for Windows 7, but that solution apparently does not work with Windows 8.
Here is the link to the Windows 7 solution Adding Eudora to Windows 7 "Default Application" list
The Windows 7 page does not mention which version of Eudora is being used, so that may be my problem. I am using Eudora 5.2.
However, as mentioned in the Windows 7 solution, Eudora 5.2 does have a setting to provide a warning if Eudora is not the default email program when it is started, and I have tried unchecking and checking the setting multiple times, including while opening Eudora as administrator. However, the warning never appears and Eudora never gives me the option to set Eudora as default.
Also, after trying the solution for Windows 7 multiple times, Windows 8's "default programs" dialog continues to not show Eudora as an option (it only shows one radio button for the default email application, "Use my current e-mail program," which is apparently the Windows Mail application).
As a result, if I click on an email link on a web page Windows Mail opens and wants me to set up an account, which I do not want to do. Windows Mail then stays open until I use Task Manager to kill it.
Any help will be appreciated.