swoosh_domain_router

# SwooshDomainRouter

`SwooshDomainRouter` is a small Swoosh adapter that delegates email delivery
according to the exact domains of envelope recipients. It is intended for
staged deployments where selected test domains should remain in a local
mailbox while real recipients receive email through a production provider.

The package has no Phoenix or Ash dependency. A Phoenix application may expose
the normal Swoosh local mailbox separately.

## Installation

Add `swoosh_domain_router` to your list of dependencies in `mix.exs`:

```elixir
{:swoosh_domain_router, "~> 0.1.0"}
```

## Configuration

```elixir
config :my_app, MyApp.Mailer,
  adapter: SwooshDomainRouter.Adapter,
  routes: [
    [domains: ["example.com"], adapter: Swoosh.Adapters.Local]
  ],
  fallback: [
    adapter: Swoosh.Adapters.Resend,
    api_key: System.fetch_env!("RESEND_API_KEY")
  ],
  mixed_recipients: :error

config :swoosh, :api_client, Swoosh.ApiClient.Req
config :swoosh, local: true
```

The router does not depend on any delivery provider. Replace `:fallback` with
any Swoosh adapter configuration:

```elixir
# Static Amazon SES credentials; the consuming application must include :gen_smtp.
fallback: [
  adapter: Swoosh.Adapters.AmazonSES,
  region: System.fetch_env!("AWS_SES_REGION"),
  access_key: System.fetch_env!("AWS_SES_ACCESS_KEY_ID"),
  secret: System.fetch_env!("AWS_SES_SECRET_ACCESS_KEY")
]

# ExAws-managed SES credentials, for instance-role or service-specific config.
fallback: [
  adapter: Swoosh.Adapters.ExAwsAmazonSES
]
```

Provider-specific optional dependencies belong in the consuming application.
Both Swoosh SES adapters require `{:gen_smtp, "~> 1.0"}`; the ExAws variant
also requires `:ex_aws`.

The router evaluates all `to`, `cc`, and `bcc` recipients. Domain matching is
case-insensitive and exact: `user@example.com` matches `example.com`, while
`user@example.com.attacker.test` does not.

Messages containing recipients for multiple destinations return
`{:error, :mixed_recipient_routes}`. Splitting such an email is intentionally
not supported because a copied or blind-copied recipient should not change the
delivery safety policy.