Apple Mail 11.5 sometimes does not remove emails from POP after 1 week
I have been using Apple Mail for years and most of the time it does as it's supposed to, but just occasionally it leaves emails on my POP server and I can't figure out why. This is annoying as occasionally those emails mount up and fill my inbox so any further emails get rejected, and if it's an important email this is bad.
I have the email server settings for the account to remove emails after 1 week, most of the time this works fine. If I click the 'Remove now' button this works but I really shouldn't have to do this.
I tried logging out and back in (on my Mac) but it made no difference. Sometimes MacOS / Mail will lose authority for certain functions so a logout / login is necessary (why? I have no idea! Authority should remain so long as I am logged in as far as I'm concerned, my screen locks after a few minutes and requires a password to unlock).
Thank you for any advice.