# Routing plugin (/docs/plugins/built-in/routing)



`routingPlugin` centralizes application routing rules without hiding fallback behavior inside an adapter.

```ts title="src/email.ts"
import { routingPlugin } from "@opencoredev/email-sdk/plugins/routing";

const email = createEmailClient({
  adapters: [primary, transactional],
  plugins: [
    routingPlugin({
      select({ message, options }) {
        if (options?.metadata?.tenant === "enterprise") return "primary";
        if (message.tags?.some((tag) => tag.name === "receipt")) {
          return "transactional";
        }
      },
    }),
  ],
});
```

The selector may be async. Returning `undefined` preserves the caller's adapter choice or the client default. Returning a name sets the primary adapter; normal retry, validation, and fallback rules still apply.

## Keep rules deterministic [#keep-rules-deterministic]

Route from data already present in the message or send metadata. Avoid network calls in the selector because they delay every send and can fail as `EmailMiddlewareError` before provider validation.

A routing plugin does not register adapters. Every returned name must already exist on the client.

<Card title="Delivery capabilities" href="/docs/adapters/capability-groups" description="Make sure every selected route preserves the required behavior." />

<Card title="Fallback and retries" href="/docs/concepts/fallbacks-and-retries" description="Understand what happens after the primary route fails." />