When I've created a folder with subfolders in BT mail on my iPhone, the folders don't show up in the desktop version of BT mail. Can anyone tell me what I need to do to make it sync, or is it not possible to do? I wondered if it it might be like Spotify where you have to to log out of both devices to make any changes that show on both, but that doesn't seem to work.
Presumably you are using a mail client (app) on one or both devices rather than webmail. Make sure the client(s) is (are) configured as IMAP rather than POP3.