Best way to migrate dovecot emails to cpanel

Hey I have about 7000 email addresses to transfer from a single Dovecot server. The mail transfer itself was successful and I can read the messages through Roundcube. The problem has become that all the messages are unread. Dovecot uid-list and filenames match each other, so the problem is probably not there. There is an S flag in the file names, which should mark the message as read. However, this is not what it does. If I go to open the message, S:2:S appears in the file name I can't use imapsyc because I don't know the email login information. The migration should be as inconspicuous as possible for the end user