Unless you've done something unusual with the IMAP account, any email message you have, no matter how old, remains resident on the server until and unless you delete it.
Email is not like files and folders, it's not a simple copy and paste.
What are the settings (and you can anonymize your address & password, it's the server settings, including checkboxes that are key, and really only for incoming messages) for the POP account?
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
There are many who labor under the gross misapprehension that the Constitution is a cage and a laundry-list rather than a framework upon which great things have been and still will be built. Many things that are entirely Constitutional are not "in the Constitution," but are allowed under it.