Deleted emails reappear in my inbox, why? Using macOS 10.15.7

If you use two different standards of emails you may have only deleted the local copy of the email, but left the other emails on the server.

POP stays local.

Your Mac has mailboxes that are specified on the Mac in the left sidebar.

IMAP generally is server otherwise, and same with Exchange.

edco208 Said:

"Deleted emails reappear in my inbox, why? Using macOS 10.15.7"

-------

What to do:

Reinstall the macOS:

Single Out this Mac:

Does this occur on your eMail provider's site? Does this issues occurring on other devices? Or is all only occurring on your Mac? If it is occurring only your Mac, then it is the Mac itself.

Reinstalling the macOS:

Sometimes, when major changes are made to your Mac(i.e. update installations), system settings (i.e. for Mail) become manipulated, technically. So, when reinstalling, nothing would be deleted. It's just that items that have become corrupted or deleted, would be replaced or reinstalled back to where they should be. Go Here: How to Reinstall macOS from macOS Recovery - Apple Support

Important: First, Back Up your Mac:

Create a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the reinstall.