I have an SBS2011 server running Exchange 2010 SP3 which has a Mailbox Database that I want to reduce in size. I have removed several old users and their mailbox and active users have deleted a large amount of data from their deleted items. I have set the "Keep deleted items" to 0 days on the Mailbox database from the Limits tab under Organisation Configuration > Mailbox > properties but the mailbox is not shrinking. What do I need to do to shrink the store? I have run a backup.