Tutaj był problem po stronie dostawcy i jego konfiguracji IMAP,
opcja -x "." pomogła
Usage: iu-migrate -S sourceHost -D destinationHost
Optional arguments:
-i <file of usernames>
-n <number of simultaneous migration processes to run>
-L <logfile, default is migrateIMAP.log>
-t <timeout in seconds>
-u <migrate only Unseen messages>
-M <file> mailbox map file. Maps src mbxs to dst mbxs.
-m <mbx1,mbx2,..,mbxn> List of mailboxes to migrate.
-d debug mode
-I record IMAP protocol exchanges
-x <mbx delimiter [mbx prefix]> source (eg, -x '. INBOX.'
-y <mbx delimiter [mbx prefix]> destination
-a <DD-MMM-YYYY> copy only messages after this date
-b <DD-MMM-YYYY> copy only messages before this date
-U update mode, don't copy messages that already exist at the destination
-H use an MD5 hash of the message body to determine uniqueness
-T copy custom flags (eg, $Label1,$MDNSent,etc)