Using older versions of Outlook for Mac in business environments
The simplest solution is to set your Yahoo account up as an IMAP account. That means you keep all your emails on the Yahoo server and you can access them either directly on a browser like Safari or any other browswer you prefer or you can view and work with them on an email client like Outlook, Apple mail or any other email app of your choice - and I believe there are many. Alternatively if you want to keep actual email files on your hard disk you can drag and drop them directly out of Oulook onto a folder on your Mac's hard drive. This will create a file with an .eml extension that can be opened by many email clients that are available. But then you have no sync between these files and an email client so it is not a great solution. I have found Mac's Time Machine very reliable albeit it a bit clunky to work with, over may years of backup to a hard drive. I don't use Apples iCloud for this as I find it quite costly and as I have a terabyte of free storage with my 365 subscription it does not make sense to also invest in an iCloud facility.