Good news: you can still build and test apps using the Email Service! If you’re on the Free plan, you’re always in Test Mode – this means all emails are redirected to the email address associated with your Anvil account – but they still send! Perhaps the docs should make this more clear 
Plus, of course, as is mentioned up-thread, you can sign up for a free external email provider and use them if you want; we just really do not want to deal with the hassle of “being a free account to send email from”.