Did you already try google?

One of the first hits:

http://www.linuxquestions.org/questions/linux-newbie-8/import-mail-from-kmail-to-opera-696088/


On Thu, Sep 30, 2010 at 10:58 AM, Paul Stear <gentoo@appjaws.plus.com>wrote:

> Is it possible to copy the kmail mail folders/messages so that they can be
> read by opera's mail client?
> Thanks for any replies
> Paul
>
>
> --
> Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
>
>