Modifying Mailbox Rentention policy on Exchange 2007 Server Stores. By default mailbox retention policy of Exchagne 2007 Store is 30 days. you can modify this as per the requirement.  Below command helps to modify all the store

Get-Mailboxdatabase | Set-MailboxDatabase -MailboxRetention 10

Below command will set the Mailbox retention policy on the specified exchagne server to 10 days

Get-Mailboxdatabase | |?{$_.ServerName -eq <servername>} | Set-MailboxDatabase -MailboxRetention 10