This is in the reference to the order placed at our company. We received your order for (item and number) and wish to thank you.
This item is presently back-ordered and we are unable to send it to you on the immediate basis. If, due to this unfortunate delay, you would like to cancel your order, please send us a note to that effect. Otherwise, you can expect delivery in approximately (time).
We deeply regret the delay. Please accept our apology for this delay.