[Dovecot] BestPractice to migrate imap mailbox from one machine to another

Hi list,

currently I use dovecot v1.2.15 with maildir++ mailboxes. (Debian Squeeze) I want to set up a different server with dovecot v2, also maildir++ mailboxes. (also Debian Squeeze)

What is the best way to copy the existing mailboxes from the older machine running dovecot v1.2.15 to the new naked machine?

Greetz, Tobias