Add new folder to iCloud mailbox.

I am wondering if one can add a folder to their icloud mail account. Folders are - Inbox, Drafts, Sent, Junk, Trash, Archive and icloud saved mail. Is there another way to add another folder? Asking for my husband who wants a folder for his work related email that is not his work address.

He wants to send it to himself and have a special folder to put it in.

I did receive one reply that told me to click on ‘New Mail Box’ on the bottom right hand corner of the mailbox screen but NO WHERE on the mailbox screen does it say ‘new mail box’

Thanks!!