LargeItemLimit: migration fails on large items

Why it happens

A large item is a message in the source mailbox that exceeds the target mailbox's maximum message size (or the organisation-wide value if the mailbox has none set). LargeItemLimit defaults to 0, which means the request fails if any large item is found. Microsoft has deprecated LargeItemLimit in the cloud service: admins now review the Data Consistency Score and skipped items instead.

Where you see it, and what it affects

A large item is counted against the target mailbox's maximum message size when you migrate to Exchange Online or between on-premises Exchange servers. In the cloud service the LargeItemLimit parameter is deprecated, so large items now show as skipped items in the migration batch details in the Exchange admin center and affect the Data Consistency Score. On-premises, in Exchange Server 2013, 2016, 2019 and Subscription Edition, the parameter still applies to New-MigrationBatch and the request fails when the limit is exceeded.

How to fix it

1. 1

   Step 1

   For cloud migration batches, check the Data Consistency Score and the skipped items list, then approve the skipped items if the loss is acceptable.

2. 2

   Step 2

   For on-premises move requests that still use the parameter, set LargeItemLimit to a small value (Microsoft recommends 10 or lower) and resume.

Get-MigrationUserStatistics -Identity user@contoso.com -IncludeSkippedItems | Select-Object -ExpandProperty SkippedItems

Check that it is fixed

• In the Exchange admin center, go to Migration, select the batch and select View details. Check the Items Skipped and Data consistency score columns for the user.
• Run Get-MigrationUserStatistics -Identity user@contoso.com | Format-List SkippedItemCount,SkippedItems to see how many items were skipped and why.
• When the move finishes, the user's status should be Completed.

Sources

Full guide: How to migrate from Exchange Server to Exchange Online →