Would be super handy if in the 'print/email invoice' window you could add the option to display the 'customer purchase order number' column, along with invoice number, date, customer etc. similar to ...
Yes when i go to Email an invoice to a customer i will add our Packing slip number/Job Number and there order number to the Subject line, This gives the invoice complete taceability and allows you to find out if a purchase order has been sent as an invoice. (ie Search sent Emails for order number)
I also update the message to make it clear who they are receiving the invoice from other wise they look like SPAM