m0b mailer

A reliable, async email microservice built with Next.js and Upstash QStash. Designed for background email delivery with retries, delays, and dead-letter handling.

✨ Features

• Async email delivery (fire-and-forget)

• Automatic retries with backoff

• Dead-letter queue (DLQ) support

• Signature verification (secure)

• SMTP-based sending (Nodemailer-ready)

🏗 Architecture

App / Backend - publish job -> QStash - signed request -> Next.js API (send-email) -> SMTP Provider

📦 Tech Stack

• Next.js

• Upstash QStash

• Nodemailer

• TypeScript

🔧 Environment Variables

QSTASH_TOKEN
QSTASH_CURRENT_SIGNING_KEY
QSTASH_NEXT_SIGNING_KEY

SMTP_HOST
SMTP_PORT
SMTP_USER
SMTP_PASS

🚀 Sending an Email

await sendMail({
  to: "<user@example.com>",
  subject: "Welcome",
  html: "<h1>Hello</h1>",
});

Returns a QStash message ID for tracking.

🔁 Retries

Configured during publish:

retries: 5,
retryDelay: "30", // seconds

• Retries on non-2xx responses

• Exponential backoff

• No manual retry logic needed

☠️ Dead-Letter Queue (DLQ)

• After all retries fail, QStash calls:

POST /api/v1/send-dlq

• The DLQ endpoint:

• Stores failed payloads

🔐 Security

• All worker endpoints use QStash signature verification

• Prevents unauthorized requests

• Safe for public deployment

📜 License

MIT