Hi @Anon4343 ,
emails may have been deleted from the mailbox
I wonder if this email was deleted from the deleted item for more than 14 days?
If not , I would suggest you could refer to this link to create a content search in the Microsoft Purview compliance portal.
And please refer to the screenshot below to enter cc parameter in the conditions. This will search for all mailboxes in the database that contain this message.
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