mailer.ex

defmodule ApprimeReactor.Mailer do
  import ApprimeReactor.Router.Helpers

  @config domain: Application.get_env(:apprime_reactor, :mailgun_domain),
          key: Application.get_env(:apprime_reactor, :mailgun_key),
          mode: Mix.env

  use Mailgun.Client, @config

prod.exs

config :apprime_reactor,
       mailgun_domain: System.get_env("MAILGUN_DOMAIN"),
       mailgun_key: System.get_env("MAILGUN_API_KEY")

use Mailgun.Client, domain: Application.get_env(:apprime_reactor, :mailgun_domain),
key: Application.get_env(:apprime_reactor, :mailgun_key),
mode: Application.get_env(:apprime_reactor, :mailgun_mode)

defmodule MyAppMailer.Mailer do
  use Mailgun.Client,
    domain: Application.get_env(:my_app_mailer, MyAppMailer.Mailer)[:mailgun_domain],
    key: Application.get_env(:my_app_mailer, MyAppMailer.Mailer)[:mailgun_key],
    mode: Application.get_env(:my_app_mailer, MyAppMailer.Mailer)[:mode],
    test_file_path: Application.get_env(:my_app_mailer, MyAppMailer.Mailer)[:test_file_path]

  @from "noreply@my_app.io"

  defp deliver(opts) do
    send_email(opts)
  end
end

config :logger, level: :info

config :my_app_mailer, MyAppMailer.Mailer,
  mailgun_domain: System.get_env("MAILGUN_DOMAIN"),
  mailgun_key: System.get_env("MAILGUN_KEY")

defmodule ApprimeReactor.Mailer do
  import ApprimeReactor.Router.Helpers

  use Mailgun.Client,
    domain: Application.get_env(:apprime_reactor, ApprimeReactor.Mailer)[:mailgun_domain],
    key: Application.get_env(:apprime_reactor, ApprimeReactor.Mailer)[:mailgun_key],
    mode: Application.get_env(:apprime_reactor, ApprimeReactor.Mailer)[:mode],
    test_file_path: Application.get_env(:apprime_reactor, ApprimeReactor.Mailer)[:mailgun_test_file_path]

config :apprime_reactor, ApprimeReactor.Mailer,
  mailgun_domain: System.get_env("MAILGUN_DOMAIN"),
  mailgun_key: System.get_env("MAILGUN_API_KEY")