Mail not downloading new email from POP account
Mail (16.0 on Ventura) has suddenly stopped getting new emails from my POP account provider. There's no error messages and when you manually check it says 'no new mail', but I know there is mail from IMAP on my phone.
I've tried changing the password to something wrong and there's no error, so it doesn't look like Mail is actually making a connection and using the username/password.
I tried adding the account as a new account, but it tells me it already exists and then fails.
If I deselect the account it appears to remove all the emails from Mail, which is not what I want.
Any ideas on how to get this working or how to delete the account and re-add it without losing all my ( many years of) emails from the Mac?
iMac 27″ 5K, macOS 13.6