Contracts

Everything is contracts-first: depend on the interfaces, and rebind them in your own service provider to change behaviour.

Contract	Default binding	Swap it to…
`Contracts\Factory`	`PostalManager` (also the `postal` container alias and the facade root)	resolve connections differently (e.g. per-tenant credentials)
`Contracts\Connection`	`PostalClient` per server	wrap sends with your own instrumentation
`Contracts\SignatureVerifier`	`RsaSignatureVerifier` (raw-body RSA, fail closed)	key rotation via JWKS caching, multiple accepted keys
`Contracts\WebhookProcessor`	`StoreWebhookProcessor` (dedupe → store → dispatch)	different persistence, extra routing, metrics
`Contracts\ServerRegistry`	`ConfigServerRegistry` (reads `postal.servers`)	database-backed / per-tenant server provisioning — see Dynamic servers
`Contracts\InboundProcessor`	`StoreInboundProcessor` (dedupe → store → dispatch)	custom inbound routing or persistence

Example — custom processor that adds metrics but keeps the default behaviour:

use Cbox\LaravelPostal\Contracts\WebhookProcessor;
use Cbox\LaravelPostal\Webhooks\StoreWebhookProcessor;

$this->app->extend(WebhookProcessor::class, function (WebhookProcessor $inner) {
    return new class($inner) implements WebhookProcessor
    {
        public function __construct(private readonly WebhookProcessor $inner) {}

        public function process(string $server, $envelope): ?\Cbox\LaravelPostal\Events\PostalWebhookEvent
        {
            $event = $this->inner->process($server, $envelope);

            if ($event !== null) {
                metrics()->increment("postal.webhook.{$event->type()->value}");
            }

            return $event;
        }
    };
});

Configurable behaviour without code

Models: subclass PostalMessage / PostalMessageEvent and point postal.models.message / postal.models.event at your classes — every store read/write in the package resolves through them.
Webhook and inbound posture (path, middleware, queue, verification, store) — configuration reference.
Broadcasting on/off and channel prefix.
POSTAL_REDIRECT_TO for catching all transport mail in dev.