Sending high-concurrency transactional emails in Bun runtime using native fetch and AutoSend API

API & SMTP Integration
1

We replaced Node.js with Bun for our API gateway. How does Bun’s native HTTP client perform when dispatching transactional emails to AutoSend, and how do you structure the request handler?

2

Bun Runtime + AutoSend Native Integration

Bun includes a blazingly fast native C++ fetch implementation that requires zero external dependencies.

// server.ts (Bun)
const server = Bun.serve({
  port: 3000,
  async fetch(req) {
    const url = new URL(req.url);

    if (req.method === "POST" && url.pathname === "/api/send-otp") {
      const { email, otp } = await req.json();

      const res = await fetch("https://api.autosend.com/v1/mails/send", {
        method: "POST",
        headers: {
          "Authorization": `Bearer ${process.env.AUTOSEND_API_KEY}`,
          "Content-Type": "application/json"
        },
        body: JSON.stringify({
          from: { email: "auth@yourdomain.com", name: "Security Bot" },
          to: { email },
          subject: `Your Login Code: ${otp}`,
          html: `<p>Your single-use sign-in code is: <strong>${otp}</strong></p>`
        })
      });

      if (!res.ok) {
        return new Response(JSON.stringify({ error: "Failed" }), { status: 500 });
      }

      return new Response(JSON.stringify({ success: true }), { status: 200 });
    }

    return new Response("Not found", { status: 404 });
  },
});

console.log(`Bun server running at http://localhost:${server.port}`);

Benchmark Note: Bun’s native connection reuse completes AutoSend HTTP dispatches in under 18 milliseconds on edge infrastructure.

Relevant Documentation