# `Letterbox.Mailbox`
[🔗](https://github.com/hattoriai/letterbox/blob/v0.1.0-rc.0/lib/letterbox/mailbox.ex#L1)

The app's code that receives a message: one module for each kind
(support, replies, photographs), named in the routes
(`Letterbox.Routing`).

    defmodule MyApp.SitesMailbox do
      use Letterbox.Mailbox

      @impl true
      def process(message) do
        with %Site{} = site <- Sites.by_inbound_token(Letterbox.Address.tag(message.recipient)),
             %User{} = user <- Sites.member_by_email(site, message.verified_from) do
          Enum.each(message.attachments, &Media.add_from_email(site, user, &1))
        else
          nil -> {:bounce, :unknown_sender}
        end
      end
    end

`process/1` runs out of the request, in a job (`Letterbox.Runner`), and
gives:

  * `:ok` - done: the message is `"delivered"`;
  * `{:bounce, reason}` - refused, for good: the message is `"bounced"`,
    and not tried again;
  * `{:error, reason}`, or an exception - it is tried again, up to
    `:max_attempts` times, then `"failed"`.

Anything else is `:ok`. A mailbox is tried again with the same message,
so what it does should be safe to do twice (an attachment kept twice is
one file, with Storehouse's `:existing`).

# `process`

```elixir
@callback process(Letterbox.Message.t()) ::
  :ok | {:bounce, term()} | {:error, term()} | term()
```

---

*Consult [api-reference.md](api-reference.md) for complete listing*