Unable to Create Mailbox: The mailbox couldn't be created on the server

The iPhone users Guide IOS 15 "Organize your email", Use mailboxes to organise emails on your iPhone, iPad or iPod touch – Apple Support (AU), and my own intuition suggest going to [Mailboxes] selecting [Edit], selecting [New Mailbox] to create a new mailbox. No other instructions or requirements are listed, very simple instructions.

The suggested actions do not create a new mailbox. The error message is: "Unable to Create Mailbox: The mailbox couldn't be created on the server. " The server is not the place for the mailbox. The Mailbox should reside on the iPhone.

Some of the 600 plus Community/Support articles on this subject suggest email must be setup with IMAP instead of POP3. Eyesfly got an answer like this is discussions.apple.com/thread/253594540. Maybe there are other settings that might have an impact on the simple instructions.

Besides looking for information/solutions, the email account has been deleted and re-installed with no change in response. The new mailbox was also added to the Email account via web access not on the iPhone. POP3 really shouldn't make any difference but since there seems to be a hybrid POP3/IMAP working, that was attempted.

I'd really like to find a definitive solution to this problem. Any clarifications someone can provide will be much appreciated.

iPhone 13 mini

iOS 15.4.1