Now we'll discuss how to configure the deleted mailbox retention period in Exchange Server 2007
Run the following command in Exchange Management shell,Set-MailboxDatabase dbName -MailboxRetention 32.00:00:00
dbname - specifies database name,
32.00:00:00 - specifies the retention period, i.e., the number of days, hours, minutes, and seconds required for it.
By default, deleted mailboxes are retained for 30 days before they are purged from the mailbox database.