You may archive emails to your computer if your Inbox grows too large. These are the guidelines for using Microsoft Outlook.

1. Configure the account in Outlook as IMAP (if not already done)
2. Choose your top-level Outlook folder (perhaps the Inbox) after setting up, then click FILE...ARCHIVE.
3. Check the box next to Archive this folder and all subfolders.
4. Be careful to specify the date to archive emails older than today.

For the archived email, a new PST will be created as a result.

Note: You may need to run the Archive TWICE if you have a bigger email box.

5. Use FILE | OPEN | Outlook Data File... and choose the Archive pst if, after completing it, the Archived Folders section in Outlook does not appear.
6. You're done

https://www.shoviv.com/blog/import-outlook-emails-to-gmail/
https://www.shoviv.com/blog/how-to-import-outlook-to-thunderbird/
https://www.shoviv.com/blog/how-to-download-emails-from-yahoo-to-computer/