The HTML email is great when you only want your client to see your custom Invoice. The other issue is this email contains a logo from some unknown source location and is not removable or changeable.

The Online invoice option in the Online Delivery email still gives the client an option to download the QuickBooks version of the invoice. This is confusing because it should only download any attachments you are allowing. Please remove the download/view invoice when you opt out of it and replace it with what you allow as an attachment.