Routing plugin

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

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

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.