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 occurs when we are unable to find or access an item in the target mailbox.
“Failed to process 8 items” refers to the batch-level processing of messages during the migration.
This scenario can occur when items that were previously migrated successfully are later deleted from the target mailbox, while changes are made to the corresponding items in the source mailbox (for example, adding a reaction such as a thumbs up or other modification).
During a subsequent synchronization in Mail Sync mode, the system detects that the source item has been updated. However, since the corresponding item no longer exists in the target mailbox, there is nothing available to update, which results in the above error being generated.
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.
