mailer.ex

defmodule MyApp.Mailer do
  @from "[email protected]"
  @mailer_impl Application.fetch_env!(:my_app, :mailer)

  defmodule Behaviour do
    @callback send_mail([key: String.t]) :: :ok
  end

  def send_test_mail(email) do
    :ok = @mailer_impl.send_mail(
      to: email,
      from: @from,
      subject: "Test!",
      text: "Test from MyApp"
    )
  end
end