On my Mac I accomplish email backups using the Mail app and Chronosync. I have filtering rules to automatically file messages into multiple IMAP mailboxes based on sender or subject. I periodically manually move messages older than a week to local mailboxes to keep my iCloud storage from getting large enough to require paying for additional storage. The Mail app can also export those local mailboxes to a folder which I then back up using Chronosync so I have local copies on multiple drives.

The whole process only takes about 5 minutes once every week or two. It gives me easy access to over 20 years of email which is nice to have even though I only search the old ones a few times a year.