Seeing item-level errors in MigrationWiz does not necessarily mean the mailbox job failed. MigrationWiz is designed to continue processing even when certain items cannot migrate.

When the service hits problems such as a corrupted IPM message, an oversized item that exceeds the destination tenant message size limit, or a malformed iCalendar entry, it records the failure at the item level, logs it in the error report, and keeps moving through the rest of the batch. The parent job continues running.

That behavior is intentional: one bad calendar appointment should not prevent 15,000 valid messages from migrating. The tradeoff is that Completed does not automatically mean everything migrated. A job can finish with a completed status while still having 200 failed items that users may later report missing.

To close that gap, post-migration auditing should include exporting the item-level error report from MigrationWiz, sorting failures by error code, and deciding which ones need manual remediation versus which reflect genuine source-side object corruption with no migration path.

Are you pulling and categorizing MigrationWiz item-level error reports after every batch completes?

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