Because of security issues I ultimately had to set up a new account with a new password to enable this both on the server and on my Mac. Which meant unfortunately I lost all my old emails to this account. What I now learn is that if you set up an IMAP account instead of a POP account the mailbox automatically sets up archive mailboxes in the "on my mac" section e.g. "bulk mail, draft, sent and trash", that act as depositories of emails you might want to keep. That is obviously what I should have done first before deleting the account then all my old emails would have been saved locally. Also interestingly once you move any emails from the IMAP mailboxes to the "on my mac" mailboxes the emails are deleted on the server which happens automatically if the account is a POP account. This is because IMAP account emails are not deleted on the server unless instructed to do so by accessing the server via a web account and deleting. I hope this helps anyone with the same problem as I had and which you learn from. 🙂
