How can I enable retrieving messages within 7 days of receipt in Exchange to use Instant Replay?

You can’t disable Exchange’s duplicate detection system altogether, but you can change how long its database keeps email entries. To change the default setting of 7 days, you will need to modify the DeliveredTo Expiration in Hours value. By replacing 7 days with 1 hour or so, you’ll be able to use Instant Replay whenever it works for you.