# `Mailglass.Compliance`
[🔗](https://github.com/szTheory/mailglass/blob/v1.0.0/lib/mailglass/compliance.ex#L1)

Injects RFC-required and mailglass-specific headers into outbound messages.

Phase 1 ships functional stubs for the v0.1 RFC floor:

  * `Date` — RFC 2822 format; injected if absent.
  * `Message-ID` — RFC 5322 unique identifier; injected if absent.
  * `MIME-Version` — always `"1.0"`; injected if absent.
  * `Mailglass-Mailable` — `"Module.function/arity"`; injected if absent.

Full RFC 8058 `List-Unsubscribe` + `List-Unsubscribe-Post` lands in v0.5
(DELIV-01). `Feedback-ID` gets its full shape once tenant-scoped streams land
in Phase 2.

## Invariant

`add_rfc_required_headers/1` NEVER overwrites a header that already exists.
Adopters who set their own `Date` or `Message-ID` keep their values intact.

# `add_mailable_header`
*since 0.1.0* 

```elixir
@spec add_mailable_header(Swoosh.Email.t(), module(), atom(), non_neg_integer()) ::
  Swoosh.Email.t()
```

Adds the `Mailglass-Mailable` header identifying the source mailable.

Format: `"ModuleName.function/arity"` — e.g., `"MyApp.UserMailer.welcome/1"`.

Does NOT overwrite an existing `Mailglass-Mailable` header.

## Examples

    iex> email = %Swoosh.Email{}
    iex> result = Mailglass.Compliance.add_mailable_header(email, MyApp.UserMailer, :welcome, 1)
    iex> result.headers["Mailglass-Mailable"]
    "MyApp.UserMailer.welcome/1"

# `add_rfc_required_headers`
*since 0.1.0* 

```elixir
@spec add_rfc_required_headers(Swoosh.Email.t()) :: Swoosh.Email.t()
```

Injects RFC-required headers (`Date`, `Message-ID`, `MIME-Version`) and the
`Mailglass-Mailable` header if absent.

Does NOT overwrite existing header values.

## Examples

    iex> email = %Swoosh.Email{}
    iex> updated = Mailglass.Compliance.add_rfc_required_headers(email)
    iex> Map.has_key?(updated.headers, "Date")
    true
    iex> updated.headers["MIME-Version"]
    "1.0"

# `apply_outbound_headers`
*since 0.2.0* 

```elixir
@spec apply_outbound_headers(Mailglass.Message.t()) :: Mailglass.Message.t()
```

Applies message-aware outbound compliance headers after render while stream
context is still available.

Generic RFC headers stay on the `%Swoosh.Email{}` primitive. Stream-aware
headers such as `Feedback-ID` and RFC 8058 unsubscribe headers flow through
this wrapper.

# `inject_unsubscribe_headers`
*since 0.2.0* 

```elixir
@spec inject_unsubscribe_headers(Mailglass.Message.t(), String.t()) ::
  Mailglass.Message.t()
```

Writes the RFC 8058 unsubscribe header pair atomically on the inner
`%Swoosh.Email{}`.

This is the only allowed mutation path for `List-Unsubscribe` and
`List-Unsubscribe-Post`.

# `maybe_add_feedback_id`
*since 0.2.0* 

```elixir
@spec maybe_add_feedback_id(Mailglass.Message.t()) :: Mailglass.Message.t()
```

Injects the `Feedback-ID` header into the inner `%Swoosh.Email{}` if configured and absent.

Requires a `%Mailglass.Message{}` because it interpolates the stream, tenant, and mailable.

---

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