Next.js Email Sandbox: Capture, Inspect & Test Transactional Email

npm install nodemailer
npm install -D @types/nodemailer

# Maildog sandbox SMTP — from your inbox's Integration tab
SMTP_HOST=mail.maildog.io
SMTP_PORT=2525
SMTP_SECURE=false          # false for 2525/587 (STARTTLS); true only for 465
SMTP_USER=your-sandbox-username
SMTP_PASS=your-sandbox-password
MAIL_FROM="MyApp <hello@maildog.io>"

import { NextResponse } from "next/server";
import nodemailer from "nodemailer";

// Reuse a single transport across invocations.
const transporter = nodemailer.createTransport({
  host: process.env.SMTP_HOST,            // mail.maildog.io
  port: Number(process.env.SMTP_PORT),    // 2525
  secure: process.env.SMTP_SECURE === "true", // false for STARTTLS on 2525/587
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
});

export async function POST(req: Request) {
  const { to, name } = await req.json();

  try {
    const info = await transporter.sendMail({
      from: process.env.MAIL_FROM,
      to,
      subject: "Welcome to MyApp 🎉",
      text: `Hi ${name}, thanks for signing up!`,
      html: `<h1>Hi ${name} 👋</h1><p>Thanks for signing up for MyApp.</p>`,
    });

    return NextResponse.json({ ok: true, messageId: info.messageId });
  } catch (err) {
    console.error("Email send failed:", err);
    return NextResponse.json({ ok: false }, { status: 500 });
  }
}

await fetch("/api/send", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ to: "test@example.com", name: "Ada" }),
});

// The email never reaches test@example.com. It lands in your
// Maildog sandbox inbox, where you can inspect the HTML and headers.
// Server Actions work the same way: move the sendMail call into a
// function with "use server" and call it from a form action.