How to delete user emails over 90 days old

Our IT managers have finally realized that it’s painful to move or restore Exchange mailboxes that are up to 10GB in size. They now want to enforce the use of personal folders and set mailbox limits of 256MB.

Question is, on Exchange 2003 we can set to remove deleted items after say 30 days. But is there a way (or a policy setting) to configure the server to delete ALL messages (Inbox, Sent Items, etc.) that are older than 90 days?