As I checked I also found the same issue . For this issue i have made some changes
So please do it step by step . it will work for you .
Open MailboxService.php file . follow the given path :
Take backup of this file .
Copy the file from here.
Paste it in your file .
5 . Run php bin/console c:c & then php bin/console uvdesk:refresh-mailbox firstname.lastname@example.org.
hope it will work for you. if not please let me know.