I've followed your guidelines for reinstalling Apple Mail but my mac doesn't allow me to delete any mail files. It's very frustrating because my Mac keeps telling me I'm out of disk space - this is because Mail is taking up 213GB (according to 'About this Mac' storage). I've removed all email accounts and even when I had accounts added, the 'Get Info' in Finder showed they were only taking up 2.2GB.
I'm using a MacBook Pro Retina, macOS High Sierra version 10.13.6. It's two year's old. I'd love some advice on how to resolve this!