If you have Windows 10, you get automatic updates. It seems one of the latest updates to Outlook can cause a problem with a POP account. This happened after the February 16 update for Office 365 version 16.0.6568.2025.
If you have the POP account configured to leave the emails on the server, this is disregarded and deleted anyway.
If you have the POP account configured to leave all the mails on the server, emails are being duplicated. Or Triplicated. Or Quadrupled. Or even Quintupled.
You may need to uninstall the update.
Follow the instructions found here:
The Victor crew