Move AppleMail mail folders from one account to another
I want to suppress an old email-address, where I have stored all many, many mails in many folders. Unfortunately, I don't succeed in just dragging-dropping the folders (with its subfolders) into the new account in Apple Mail. Sometimes it seems to work a little bit, but most often not. It just doesn't do anything.
Any hints how I can succeed in moving the entire stock of folders to another account?
Thanks a lot.
MacBook Pro 15″, macOS 10.13