An error like this can be encountered during a mail migration, where Mail Sync is enabled: Failed to process X items: The specified object was not found in the store., Unable to open existing item for update.
The error is generated when we fail to find or access an item in the target mailbox.
"Failed to process 8 items" - It reflects on the batch processing of messages.
It can happen when someone deletes items from the target mailbox after a successful migration, but modify it later in the source mailbox. (e.g if you add emoticon to the message like thumbs up or so..). So during the new migration which ideally runs in Mail Sync mode we will detect that the source item has been updated, but there is nothing on target to be updated, and the above error is thrown.
It is strongly suggested not to make direct changes to the target mailbox while migrations are on-going. In the event changes are necessary and incremental migrations are planned, you should ensure items are in their original location in the target mailbox. Items that have been deleted should be restored to avoid errors being returned during a mailsync migration.In the event items have been removed and cannot be restored, refer to the user guide on running a new non mailsync migration task to re-migrate deleted items.
You can also download and check the migration report for the mailbox under the Reports tab in your Accounts project to get more information which items failed the migration.
