I have been using Eudora to filter all kinds of mail including list forums, and to store mail in an easily searchable database (my Eudora folder) whose files go back 20-some years.
1) Will Apple Mail or any other email app for today's Apple OS will allow this, AND allow an easy migration of files ---and mailboxes--- from Eudora? Are "Rules" in Mail the equivalent of Eudora?
2) Please send suggestions for migrating files and getting up to speed with a new App. (Is it still Apple Mail, John?) Or Postbox? MailMate? Thunderbird?
3) I am tempted to run Eudora on a dedicated old Mac so as to have easy access to all the old mail. Are there better alternatives? Preferably not too time-consuming to set up? This was maybe covered here last spring, but I don't see it. Sorry for any repetition
Try out Apple Mail instead. you can move Eudora emails to Apple Mail. I have searched this discussion for you which belongs to Apple's official discussion forum.:https://discussions.apple.com/thread/7534304
Hope that helps.