[Dovecot] Cyrus migration - Header version 6 not supported

[Arnaud Limbourg]

Hello,

I was previously running a cyrus server which I realized later on is
overkill for what my needs so I would like to switch to dovecot.

Unfortunately the cyrus2courier utility to migrate the mails gives me
the error
  Header version 6 not supported

I was using cyrus 2.2.3.

Does anybody have any advice on how I could migrate all the mails ?

Thank you.

Arnaud.