but a set of e-mail lists was created without being asked, and e-mail seems to have landed there 🙂 The show also under the uppermost boxes, '' unread" etc.

That's normal. Opera automatically detects list headers in messages, creates Mailing list views for each list. In "All Messages/Unread" (or any other view), you can click the "settings for this view" icon on the toolbar above the message list, goto "show" and uncheck "show mailing lists".

I have about 30 subfolders

IMAP subfolders? If so, that should work just fine.

if there are no way to import account settings and folder structure, I think I will have to wit untilm I have more time experimenting.

Understood. Take your time.