The administration and maintenance of Microsoft Exchange Server to ensure secure, reliable, and efficient email and collaboration services across an organization.
First of all, the PST file size must be larger than the mailbox. Even if you export an empty mailbox, you can see that the PST file size is not 0, because the file structure takes up some space.
About the recoverable items, you could use "-ExcludeDumpster" to bypass them when create export request:
For more detailed information about it, you could have a look about this article: New-MailboxExportRequest
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