Either free space doesn't become Whitespace or Exchange doesn't use Whitespace at all?

I was told that after online maintenance, some deleted space will be turned into Whitespace and Exchange will then use the Whitespace first and then start to expand the EDB file size when there is no more whitespace to use.  
But my observation supports our Exchange seems to skip using Whitespace and simply jump in to expand EDB file for use. Here is what I did:
Two days ago I moved a big mailbox of 11GB out of mdb1. With maintenance running every night I expect at least some of 11GB should turn into Whitespace if not all so the "AvailableNewMailboxSpace" should reflect the increase of whitespace. As the matter of fact, I saw the EDB file size only keeps increasing from 94G to 98G within two days. I'm wondering if the free space is never transferred into Whitespace or our Exchange doesn't use Whitespace at all.  How to fix this issue? Please help.
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Peter HutchisonSenior Network Systems SpecialistCommented:
It depends on the Keep Deleted mails setting (usually 14 days or so) and will not overwrite old mail until it gets purged. Also, the same for old mailboxes that have been deleted. Reducing these values for a few days may free up some space.
Adam FarageSr. Enterprise ArchitectCommented:
So here is the deal..

Exchange does something called "Online Maintenance" which is sometimes abbreviated out to OLM. OLM occurs around the clock in Exchange 2010 SP1 + (so Exchange 2013, Exchange 2016, ect) but it is a throttled task, so if it runs out of available resources it will stop and checkpoint the process (so when available resources are available it will resume at that point).

Now as for mailbox moves like you said, there is a completely separate retention which is the soft deletion retention (or disconnected mailbox) retention. To find that you would typically do "Get-MailboxDatabase | FL Retention". Once a mailbox move in Exchange 2010 + completes the mailbox is moved into the "soft deletion" state. By default this value is 7 days (I think, I am in the middle of rebuilding my lab) so to remove this soft deletion of the moved mailbox cannot be removed until one of two things happen:

- You use the "Remove-StoreMailbox" command
- You allow the retention period for soft deletion mailboxes to pass (e.g: disconnected mailboxes).

Remember, OLM will not reduce the physical size of an EDB but instead mark deleted data as "white space" to allow the store driver (ESE) to use the white space prior to expanding the database (why? Because it helps slightly reduce IO to write over data rather than expanding a file).

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