Whitespace not increasing when moving mailboxes to other database

Let’s try to look at this topic: White-space not increasing when moving mailboxes to other database and also more.

What is reason for it?
When a mailbox is moved to another database, it´s only softdeleted (-MailboxState SoftDeleted). This mean that its kept in the origional database until the time you have set for the database to keep deleted mailboxes (Default 30 days) has past.

Is it related also for disconnected/disabled mailboxes?
Yes, it is. Disconnected mailboxes are also still in database for retention period (-MailboxState Disabled).

How to check white-space and database size for mailbox databases?

Get-MailboxDatabase -Status| ft name,AvailableNewMailboxSpace,DatabaseSize -a

Get-ExchangeDatabaseInfo

How to find softdeleted and disabled mailboxes for particular database?

Get-MailboxStatistics -Database MBD01 | Where { $_.DisconnectReason -eq "SoftDeleted" -or $_.DisconnectReason -eq "Disabled" } | Format-List LegacyDN, DisplayName, MailboxGUID, DisconnectReason

How to purge softdeleted mailboxes and consequently increase white-space (AvailableNewMailboxSpace)?

Remove-StoreMailbox -Database MBD01 -Identity Ayla -MailboxState SoftDeleted

This example permanently purges all soft-deleted mailboxes from mailbox database MBD01.

Get-MailboxStatistics -Database MBD01 | where {$_.DisconnectReason -eq "SoftDeleted"} | foreach {Remove-StoreMailbox -Database $_.database -Identity $_.mailboxguid -MailboxState SoftDeleted}

Remove-StoreMailbox

Is it possible to remove “active” mailbox by Remove-StoreMailbox?
No, the cmdlet accepts only SoftDeleted or Disabled mailboxes.

Is there delay for white-space incrteasing after using Remove-StoreMailbox?
Yes, there is the delay, but basically only few seconds.

Is it possible restore softdeleted or disabled mailboxes?
Yes of course via New-MailboxRestoreRequest.
Softdeleted mailboxes can be only exported to existing mailbox, but disabled mailboxs can be connected and also exported same like softdeleted.

New-MailboxRestoreRequest

Connect-Mailbox

How to Reconnect a Disconnected Mailbox in Exchange Server 2010