This error indicates that your IMAP server failed to find a folder for one of the following reasons:
- The folder has been deleted
- The folder is not accessible to IMAP
- The folder has subfolders but contains no items
The last problem affects IMAP systems which are not RFC-compliant. RFC-compliant systems should return parent folders, even if they contain no items.
We recommend the following:
- Resubmit the mailbox for migration. If the offending folder was deleted, this should resolve the issue.
- Check if to see if the offending folder is exposed to IMAP. This is particularly true for Gmail/G Suite users.
- Check to see if the offending folder is empty. Consider adding a single item and resubmitting for migration.