Example of using Elixir and HTTPotion to send mail to Mailgun using the api.

mailgun.ex

defmodule Mailgun do
  @doc """
  Sends a basic message to an address. Expects a mailgun domain environment
  variable (MAILGUN_DOMIAN) and a mailgun api key environment variable
  (MAILGUN_API_KEY).
  """
  @spec mail(String.t) :: String.t
  def mail(toAddress) do
    url = "https://api.mailgun.net/v3/#{System.get_env("MAILGUN_DOMAIN")}/messages"
    headers = ["User-Agent": "Elixir",
      "Content-Type": "application/x-www-form-urlencoded"]

    params = ["from=noreply@heroku.com",
              "to=#{toAddress}",
              "subject=Missing GitHub 2FA",
              "text=Can you believe that?"]

    user = {"api", System.get_env("MAILGUN_API_KEY")}

    response = HTTPotion.post url, [body: Enum.join(params, "&"),
                         basic_auth: user,
                         headers: headers]

    case response.status_code do
      200 -> "Message queued for delivery to #{toAddress}"
      400 -> "Some kind of message error. Mailgun returned #{Poison.decode!(response.body) |> Map.get("message")}"
      401 -> "Some kind of authentication error. Mailgun returned #{response.body}"
      _ -> "Something wrong with the request"
    end
  end
end