Nothing is free. E-mail is either provided by your ISP (which you pay for) or ads are displayed alongside the e-mail messages. Facebook publishes ads. Twitter p

Nothing is free. E-mail is either provided by your ISP (which you pay for) or ads are displayed alongside the e-mail messages. Facebook publishes ads. Twitter publishes ads. Will you be publishing ads on invoices? What is your plan to have the service be sustainable into the future?