If not an emailed stamp - then perhaps after emailing an invoice, and saving the invoice, the 'To be emailed' box becomes unticked (as what happens after printing an invoice).
Provision for "stamping and dating' an emailed invoice as "emailed on ...date"
Merged
You have invoices marked as "paid" when they have been paid. I would like to see this where it is shows that an invoice has been emailed, the date it was emailed, perhaps even emailed to.
If not an emailed stamp - then perhaps after emailing an invoice, and saving the invoice, the 'To be emailed' box becomes unticked (as what happens after printing an invoice).