An example of One-Click Unsubscribe header

index.js

import { Resend } from 'resend';
import { createHash } from 'crypto';
const resend = new Resend('RESEND_KEY');

(async function() {
  try {
    const emailData = {
      from: 'Acme <onboarding@resend.dev>',
      to: ['delivered@resend.dev'],
      subject: 'hello world',
      text: 'it works!'
    };

    const unique = `${emailData.from}-${emailData.to}-${emailData.subject}-${Date.now()}`;
    const key = createHash('sha256').update(unique).digest('hex');

    const mechanisms = [
      `<mailto:[channel-slack-randomid]@[slackdomain].slack.com?subject=Unsubscribe&body=${key}>`,
      `<https://example.com/u/${key}>`
    ];
    const data = await resend.emails.send({
      ...emailData,
      headers: {
        'List-Unsubscribe': mechanisms.join(', '),
        'List-Unsubscribe-Post': 'List-Unsubscribe=One-Click'
      }
    });

    console.log(data);
    // Save data.id and key to your database
    // This will allow you to collect the unsubscribe requests and map back to the email address that requested it.
  } catch (error) {
    console.error(error);
  }
})();