Communigate Pro has a nice Migration/MoveIMAPMail utility. As Communigate is free to use for up to five accounts, I think it is legal to install it and use the MoveIMAPMail utility.
I have used it once to migrate mail from Communigate to dovecot. -- Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/
