Delete all mails from server that are not currently in IMAP mailbox

Question

For quite some time I've been using the macOS Mail application for my server-hosted email. I have my address set up through IMAP and everything has been fine up until a couple of days ago that I started getting "quota almost reached" emails. From what I understand, the mails that I have been deleting are deleted locally only but not from the server - and as a result it is now almost full.

Is there a way to delete every single email but the ones that are in my Mail app? And configure everything so that whatever I delete from there also gets deleted from the server?

Answer 1

I use Thunderbird on my Windows for all my Gmail accounts. Under the [Gmail] folder there is a Trash and a Spam folder. Rt clicking either folder yields an empty 'folder' option. Your app may have the same or similar options.