Rate Limit

async function sendWithBackoff(emailData, maxRetries = 5) {
  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      return await lettr.emails.send(emailData);
    } catch (error) {
      if (error.status === 429) {
        const retryAfter = error.retryAfter || Math.pow(2, attempt);
        console.log(`Rate limited. Retrying in ${retryAfter} seconds...`);
        await sleep(retryAfter * 1000);
      } else {
        throw error;
      }
    }
  }
  throw new Error('Max retries exceeded');
}

const recipients = [...]; // Large list
const batchSize = 50;
const delayBetweenBatches = 500; // milliseconds

for (let i = 0; i < recipients.length; i += batchSize) {
  const batch = recipients.slice(i, i + batchSize);

  await lettr.emails.send({
    from: 'you@example.com',
    to: batch,
    subject: 'Newsletter',
    html: content
  });

  // Pace your requests
  if (i + batchSize < recipients.length) {
    await sleep(delayBetweenBatches);
  }
}