Unable to append message to folder: An item we attempted to migrate was rejected by the Destination IMAP server.
This error message indicates that the item was skipped and not migrated. In most cases, you will find that the item cannot be migrated to the Destination because it is too large. If feasible, review IMAP logs at the Destination, and adjust message size limits.
If migrating to G Suite/Gmail, this error may be caused by corrupt MIME content or email items with blank subject lines. We recommend reviewing folder content and possibly filtering the folder. More information regarding this behavior can be found here: