Could you introducing a feature to allow invoices to be saved, or marked, as drafts please

I don't always use the email function within Kashflow to send out my invoices, sometimes I prefer to write a personal email and attach the invoice downloaded from Kashflow. Therefore, I can't always tell at a glance in Kashflow which invoices have been sent or not.

Would you consider introducing a feature to allow invoices to be saved, or marked, as drafts please? This feature already exists in Kashflow for Sales Orders under 'Category' when I create a new Sales Order. Could you do the same for when a new invoice is created?