In the last episode, we introduced Bamboo to send outbound emails via SendGrid. In the process, we introduced a reply-to email address for those emails. We'll let SendGrid send those replies to us and handle them in a controller to add new posts via email. Let's get started.


We're starting with the dailydrip/firestorm repo tagged before this episode.

We're taking advantage of SendGrid's Inbound Parse feature to handle inbound emails. My setup on the SendGrid side looks like this:

SendGrid Inbound Parse settings

This can only send requests to a publicly accessible URL. Right now it's set to go to the dogfood deployment of Firestorm. We can't easily get data sent to our development server, but we can write some code that handles a mock inbound request.

Let's start with a test for a FirestormWeb.Web.InboundController's sendgrid function:

vim test/web/controllers/inbound_controller_test.exs

I've already got the test ready. We'll talk through it.

defmodule FirestormWeb.InboundControllerTest do
  @moduledoc false
  @body "this is the text body"

  use FirestormWeb.Web.ConnCase
  alias FirestormWeb.{Repo, Forums}

  describe "POST /inbound/sendgrid" do
    test "creates post on corresponding thread", %{conn: conn} do
      # We'll setup some data
      {:ok, user} = Forums.create_user(%{username: "knewter", email: "", name: "Josh Adams"})
      {:ok, elixir} = Forums.create_category(%{title: "Elixir"})
      {:ok, otp_is_cool} = Forums.create_thread(elixir, user, %{title: "OTP is cool", body: "Don't you think?"})
      {:ok, yup} = Forums.create_post(otp_is_cool, user, %{body: "yup"})

      # We post to an `inbound_path`, which we still need to create.
      # I've got an `inbound_email` function that generates the json body that
      # corresponds to what SendGrid will post.
      conn =
        |> post(inbound_path(conn, :sendgrid), inbound_email(,

      assert response(conn, 200) =~ "ok"

      # Once we've confirmed that the endpoint responded with a 200, we'll
      # refetch the thread and get its last post, confirming that the body is
      # what we emailed.
      thread = Forums.get_thread!(elixir,
      thread =
        |> Repo.preload(:posts)

      last_post =
        |> Enum.reverse
        |> hd

      assert last_post.body == @body

  # Here's the JSON that SendGrid sends for each email - it parses the email,
  # and sends us a nice structured version of the data. We interpolate the
  # thread id, the `from` value and we place the the email body defined in our
  # module attribute into the `text` field.
  def inbound_email(email, thread_id) do
      "SPF" => "pass",
      "attachments" => "0",
      "charsets" => "{\"to\":\"UTF-8\",\"html\":\"UTF-8\",\"subject\":\"UTF-8\",\"from\":\"UTF-8\",\"text\":\"UTF-8\"}",
      "dkim" => "{ : pass}",
      "envelope" => "{\"to\":[\"thread-#{thread_id}\"],\"from\":\"#{email}\"}",
      "from" => "Josh Adams <#{email}>",
      "headers" => "Received: by with SMTP id hZOsSzHOPr Wed, 15 Mar 2017 18:34:02 +0000 (UTC)\nReceived: from ( []) by (Postfix) with ESMTPS id 6F27C4A1329 for <>; Wed, 15 Mar 2017 18:34:02 +0000 (UTC)\nReceived: by with SMTP id i1so28956781ota.3 for <>; Wed, 15 Mar 2017 11:34:02 -0700 (PDT)\nDKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=GwnSAhdI/u8PHC2HFrt77xzyVvP7DT+u4xmRa8rHHoY=; b=Y/Nqpsb49EiAESNhJ0eqKQDcORBW4LP2u2k9apYtQuUvPh732+gvu/Ue9fV46C4VP8 8YAnlZpBIBgeK3pXvIel2DW8cUSRotfXP6sY0vcoehVev2kJeaCYPJ/mOwLqYikbUddh gwB2CDYhD84DQGbVt1wSLfMzILpVqyiiGzHiRJUJeShuP26qsFhGifY9BUnw9ULgCKa0 NFmvfToFPrSlJU4BPtI6JjuFvjLSULJjAJJrHxfDZtCkboyV022dvp9++wxLtJLIizqg ZN8h8UHo5Mk4DVsiaP6wVVUWzB0Hn3LxJT9usqndZj2J2tSvYv7TTlQCKuIqqnQ9HbiZ 17Kw==\nX-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=GwnSAhdI/u8PHC2HFrt77xzyVvP7DT+u4xmRa8rHHoY=; b=F61cfB12rrT5PFmXkRm30gi/WFL818m1IYCS5y0Fg2GNdtwAoXr0aBBhbxodXqbIHZ fhSHfOaEP6ghdlz0BP0T4iQd060xkpIDZaJ7ei4CaSK2kMZjUPo02QBEHz6KLxOO64uw vD+bIVAzm+w65YK1b8j6g5aQ2K51mG1Ws5SrUGD61ytclY8s0mxIv+yC21Q+Ottkt4CR RojHZZwc1Gkvz90A0AfoZ4Ic/xQEpcsz4W3UoWK90VeL6Z8dbueP0/51ODTH5EtZKMkT IyavilQPGhbqRJTlzIM8DGgeeca1SgtHO+LvnhOggyLEDk2tYz9ir3uQCycNlS/1l2nM HvAQ==\nX-Gm-Message-State: AFeK/H2qEtipNG451j/+PHPcQw2JE3imo/aNif1F1vYas8j6uYeD8pBcpGjy/ZcW5YPtzwy74LzVLnmz6LNR5g==\nX-Received: by with SMTP id i14mr1762454oib.14.1489602841909; Wed, 15 Mar 2017 11:34:01 -0700 (PDT)\nMIME-Version: 1.0\nReceived: by with HTTP; Wed, 15 Mar 2017 11:34:01 -0700 (PDT)\nFrom: Josh Adams <>\nDate: Wed, 15 Mar 2017 13:34:01 -0500\nMessage-ID: <>\nSubject: test\nTo:\nContent-Type: multipart/alternative; boundary=001a113ad0403fa15d054ac93097\n",
      "html" => "<div dir=\"ltr\">testing<br clear=\"all\"><div><br></div>-- <br><div class=\"gmail_signature\" data-smartmail=\"gmail_signature\">Josh Adams<br></div>\r\n</div>\n",
      "sender_ip" => "",
      "subject" => "test",
      "text" => "#{@body}",
      "to" => "reply-thread-#{thread_id}"

So we're getting an email here that knows what thread it's meant for. All we really need to do is determine the user and create a post on that thread, and we're done. If we run the test, of course it fails because there's no such controller or route, so we'll add them:

vim lib/firestorm_web/web/router.ex
defmodule FirestormWeb.Web.Router do
  # ...
  # Inbound email routes
  scope "/inbound", FirestormWeb.Web do
    pipe_through :api

    post "/sendgrid", InboundController, :sendgrid

We can make a quick controller to handle this request:

vim lib/firestorm_web/web/controllers/inbound_controller.ex
defmodule FirestormWeb.Web.InboundController do
  use FirestormWeb.Web, :controller
  alias FirestormWeb.Forums

  @inbound_domain ""
  # Get the thread id out of something like
  # ""
  @thread_email_regex ~r/reply-thread-([0-9]*)@#{@inbound_domain}/
  # Get the email part out of something like "Josh Adams <>"
  @email_regex ~r/[^<]*<?(.*@[^>]*)[^>]*/

  def sendgrid(conn, params) do
    body = params["text"]
    from_email_param = params["from"]
    to_email = params["to"]

    with [_,from_email|_] <-, from_email_param),
         [_,thread_id|_] <-, to_email),
         # We'll need to introduce a way to get a thread just by its id - so far
         # we haven't provided that. I have no real justification here.
         thread when not is_nil(thread) <- Forums.get_thread(thread_id),
         # We also need to provide a way to get a user by email address
         user when not is_nil(user) <- Forums.get_user_by_email(from_email),
         {:ok, _} <- Forums.create_post(thread, user, %{body: body}) do
           # FIXME: Post created successfully, maybe I want to instrument this
           # in the future.
      _ ->
       # FIXME: Maybe I want to report failures to a logging service here.
    send_resp(conn, 200, "ok")

We always send a successful response because I really don't know what else to do in this situation, no reason for SendGrid to concern themselves with it. I've also stubbed out the ability to add instrumentation and logging, but we really don't have a good use for this yet.

Next, we'll add the missing functionality to our Forums context:

vim lib/firestorm_web/forums/forums.ex
defmodule FirestormWeb.Forums do
  # ...
  @doc """
  Gets a single user by email address. Maybe.
  def get_user_by_email(email), do: Repo.get_by(User, %{email: email})
  # ...
  @doc """
  Gets a thread by id.

  Maybe returns a thread.
  def get_thread(id) do
    |> Repo.get(id)
  # ...

At this point, all of our tests pass. Once this is deployed, if we have SendGrid set up correctly, we'll receive new emails to this endpoint via their webhooks and we'll insert a new post from the user associated with that email address!


Today we quickly saw how we can handle inbound emails using SendGrid's Inbound Parse service to allow users to reply to threads from their email provider. Right now we'll also include any quoted details in the reply in our post, which is kind of awful. We'll fix that later. See you soon!