convert mbox -> maildirs

[Enrique Vadillo]

I'm switching more than 15.000 users to Qmail using maildirs,
i'd like to know what is the best tool i can use in order to
convert /var/mail/user mboxes into ~user/Maildir format and to
convert ~user/Mail/folder into ~user/Maildir/.folder format too.

thanks!

Enrique-