@021.is/spine-email

Resend wrapper. Bearer auth, retry on 5xx, terminal on 4xx (no infinite-loop on permanent client errors), idempotency-key passthrough, structured logging hook.

Use

import { makeEmailClient } from "@021.is/spine-email";

const email = makeEmailClient({
  apiKey: env.RESEND_API_KEY,
  defaultFrom: "My App <[email protected]>",
  retries: 2,
  logger: console, // optional pino-compatible logger
});

await email.send({
  to: "[email protected]",
  subject: "Welcome to My App",
  html: renderToString(<WelcomeEmail name="Sam" />),
  tags: { app: "my-app", flow: "signup" },
  idempotencyKey: `signup-${userId}`,
});

Behavior

• 5xx → up to retries more attempts (default 2)
• 4xx → throws SomethingWentWrongException immediately, no retries (4xx is permanent — looping wastes time + money)
• Missing both html and text → throws
• Sets idempotency-key header when provided (Resend dedupes server-side)

React Email templates

Templates live in the consuming app (React Email, MJML, plain HTML — your call). spine-email is just the transport.

Why not just fetch

Default fetch has no retry, no logging, no terminal-on-4xx logic, no idempotency. After the third app reimplemented it, it became a package.