How can I send a promo only to the new DJ's I have just added to my promo list?

When you send a promo out without ticking "Reminder" or "Resend" the system works in Standard mode.

Standard Mode will send a promo to any DJ Recipient who has never received that promo before. It will automatically filter out DJ Recipients who have already received your promo so it works brilliantly if you want to send a promo just to the new DJ Recipients that you have recently added to your promo lists.