1. Go to Sales > Point of Sale (POS).
2. Assign a customer to the POS order.
   • Click Customer  , then search for a customer or click +New customer to a create a new one. 
     
   • Make sure the selected customer has a valid email address set in their profile.
3. Click Pay.
4. Tick Email eReceipt before clicking Pay now.
    

Yes - here's how to do it:

1. Go to Sales > Invoices & credits.
2. Open the invoice by clicking on its invoice number.
3. Click Actions, then select Email eReceipt.
   
4. Make sure the entered email address(es) are correct before clicking Send.