When you delete a mailbox, Exchange retains the mailbox in the mailbox database and switches the mailbox to a disabled state. The associated Active Directory user account is also deleted. The mailbox is retained until the deleted mailbox retention period expires, which is 30 days by default, and then it's permanently deleted (or purged) from the mailbox database.
Until a deleted mailbox is permanently deleted from the Exchange mailbox database, you can use the EAC or the Exchange Management Shell to connect it to an Active Directory user account. You can also use the Exchange Management Shell to restore the contents of the deleted mailbox to an existing mailbox.
For more information, see Connect or restore a deleted mailbox
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