If you send the invoice yourself outside of QuickBooks, you cannot mark the invoice as sent as this is updated automatically by the system. You can CC yourself in under the customer email box when creating an invoice - you can then fill out your email address in the box. If you would like to be CCd in every time you send an invoice, you can go to the cog wheel > account & settings and then click Sales. Scroll down and click on the Messages section, here there is a section for 'Copy (Cc) new invoices to address'.
You are in the right section, below the default email in the messages section there should be a tick box and something which says email me a copy and it will have prefilled in your email. If you tick that and then save it will then auto cc you into to any invoices sent
Any questions let us know
Ah, it looks like you are using the Self Employed product - apologies, I thought you were using our Online product! Unfortunately this is not a feature of our self employed account - please use our feedback link https://selfemployeduk.uservoice.com/ to suggest for them to implement this in future updates.