Migrating from btinternet mail to icloud mail

Please be gentle and forgiving as I'm sure this has been asked before but I can't find it and although I'm not tech averse I'm no tech nerd either.

After many years with a btinternet email address I've decided to switch broadband provider and ditch BT. I've been using the btinternet address in Apple mail on Mac, ipad, iphone for years and have lots of folders set up (time for some housekeeping I think). When I've created an icloud email address is it possible to migrate the emails in the previous address to the new address and to keep the folders intact? If it is please help with the process. Many thanks