Mailgun

const mailgunSdk = require('mailgun-js');
const apiKey = process.env.MAILGUN_API_KEY;
const domain = `mail.${process.env.DOMAIN}`;
const mailgun = mailgunSdk({ apiKey, domain });

export default async (req, res) => {
  let response;

  try {
    response = await mailgun.messages().send({
      to: req.body.to,
      from: req.body.from,
      subject: req.body.subject,
      text: req.body.text
    });
  } catch (error) {
    return res.status(error.statusCode || 500).json({ error: error.message });
  }

  return res.status(200).json({ result: response.message });
};

Usage

First, create a Mailgun account. Then, retrieve your API key.

If you want emails to come from your email address, you'll need to add a domain. Don't want this right now? Use the sandbox domain.

To securely access the API, we need to include the secret with each request. We also do not want to commit secrets to git. Thus, we should use an environment variable. Learn how to add environment variables in Vercel.