Hi Pete,
We have a browser based sales management (SOP) add-on called BluWare for GP that handles this feature you are talking about.
We allow for pre-set email addresses at the customer and/or address level and we also let you override email addresses at the time of order entry.
Combined with these features, we can automate the distribution of order acknowledgements or almost any other report based on workflow or status updates of the order.
If I can get you any other information send me an email and I can provide you with some more details.
Thanks,
Adam