Symptoms

You recover Microsoft 365 data from a backup (via Online Dashboard).

Entire mailbox is selected for recovery.

After recovery, the operation status is "succeeded with warnings":

Cannot recover Microsoft 365 mailbox item ID: ..... in folder .... is skipped because size is larger than 4MB limit.

Data is recovered successfully except the attachment mentioned in the warning.

Cause

Microsoft 365 limitation:  letters that contain attachments that are larger than 4MB cannot be restored.