Choose properties and click the Limits Tab.Click on the respective Mailbox Database that you want to verify.Select the Database Management tab in the Mailbox pane.Expand Organization Configuration and select the mailbox for which you want to verify the retention policy.Go to Exchange 2010 Management Console and expand Microsoft Exchange On-premises in the navigation pane.Follow the below steps to verify the retention policy:

So, if you want to reconnect a mailbox, then you should verify the deleted mailbox retention policy. However, when the retention period ends, the mailbox will be deleted permanently. You can reconnect any deleted mailbox during this period. When you accidentally delete a mailbox in Exchange 2010, it gets disconnected from your account and held in the directory for 30 days which is the default mailbox retention period. But, the relieving part is that a mailbox is never removed permanently from Exchange 2010. Recovering an Exchange mailbox that is deleted accidentally can be one of the most frustrating things for a user as with the deletion of the user mailbox, its associated user account also gets deleted.

Exchange 2010 deleted items recovery