delete email prior to ex2013 migration

I am migrating to exchange 2013 from ex2007sp3.  Prior to moving mailboxes to the ex13 server, I have been tasked with deleting messages from the Exch2007sp3 database older than 90 days. 

This is my pshell cmd so far:

Get-Mailbox -Database "private information store" | Export-Mailbox -EndDate “1/1/2015” -ExcludeFolders "\Calendar" -DeleteContent -BadItemLimit 100

I plan to change the Delete Item Retention to 0 days so that the messages are truly gone.

Does anyone have a better suggestion?

 Thanks