[Dovecot] transfer files from Plesk qmail to Dovecot and Postfix

I have some files I want to transfer from Plesk qmail to Postfix with virtual mailboxes, MySQL, Maildir etc.

I can add the accounts to the database manually as there are only a few of them. In the case of the mail folders, is it merely a matter of copying the mail files over, or are there some adjustments to be made to the files?

I have noticed the thread about the Courier to Dovecot script and I wonder whether it may have a role in this process.