Bulk Sending

Sendr has two approaches for sending at scale:

Approach	Best for	Max per call
Batch endpoint	Transactional bulk (order updates, notifications)	100 emails
Campaigns	Marketing broadcasts to audiences	Unlimited (via audience)

Batch endpoint

The /v1/emails/batch endpoint accepts up to 100 emails per request and queues them atomically. All emails in a batch share a default from, subject, and template_id, with per-email overrides.

Basic batch

import { Sendr } from "sendr";

const sendr = new Sendr(process.env.SENDR_API_KEY!);

// Build your list of recipients
const users = [
  { email: "alice@example.com", name: "Alice", orderId: "ORD-001" },
  { email: "bob@example.com", name: "Bob", orderId: "ORD-002" },
  // ... up to 100
];

const { data } = await sendr.emails.sendBatch({
  from: "orders@acme.com",
  subject: "Your order has shipped",
  emails: users.map(user => ({
    to: user.email,
    html: `<p>Hi ${user.name}, order ${user.orderId} has shipped!</p>`,
  })),
});

console.log(`Queued ${data.length} emails`);

Large lists: chunk into batches

function chunk<T>(array: T[], size: number): T[][] {
  const chunks: T[][] = [];
  for (let i = 0; i < array.length; i += size) {
    chunks.push(array.slice(i, i + size));
  }
  return chunks;
}

async function sendToAllUsers(users: User[]) {
  const batches = chunk(users, 100); // Max 100 per batch
  const results: string[] = [];

  for (const batch of batches) {
    const { data } = await sendr.emails.sendBatch({
      from: "hello@acme.com",
      emails: batch.map(user => ({
        to: user.email,
        html: `<p>Hi ${user.name}!</p>`,
      })),
    });
    results.push(...data.map(e => e.id));

    // Brief pause to avoid hitting rate limits
    await new Promise(resolve => setTimeout(resolve, 200));
  }

  return results;
}

Batch with templates

Use template_id for a shared template and variables for per-email substitution:

await sendr.emails.sendBatch({
  from: "hello@acme.com",
  template_id: "tmpl_abc123",
  emails: users.map(user => ({
    to: user.email,
    variables: {
      name: user.name,
      plan: user.plan,
      expiry: user.expiresAt,
    },
  })),
});

Campaigns

For marketing broadcasts to large audiences, use campaigns. Unlike the batch endpoint, campaigns:

• Target an entire audience (contact list) rather than individual addresses
• Handle unsubscribes automatically via List-Unsubscribe headers
• Can be scheduled in advance
• Provide per-campaign analytics

Campaign workflow

// 1. Create an audience
const audience = await sendr.audiences.create({
  name: "Pro Plan Users",
});

// 2. Add contacts to the audience
await sendr.contacts.bulkImport([
  { email: "alice@example.com", first_name: "Alice" },
  { email: "bob@example.com", first_name: "Bob" },
  // ...thousands more
]);

// 3. Create and schedule the campaign
const campaign = await sendr.campaigns.create({
  name: "March Feature Announcement",
  subject: "New features in March",
  from: "Newsletter <news@acme.com>",
  audience_id: audience.id,
  html: `
    <h1>Here's what's new in March</h1>
    <p>We shipped three major features this month...</p>
  `,
  unsubscribe_url: "https://acme.com/unsubscribe",
  scheduled_at: "2025-03-15T09:00:00Z",
});

console.log(campaign.status); // "scheduled"

// 4. Check stats after sending
const stats = await sendr.campaigns.getStats(campaign.id);
console.log(`Delivered: ${stats.delivered} / ${stats.total}`);
console.log(`Open rate: ${((stats.opened / stats.delivered) * 100).toFixed(1)}%`);

Cancelling a campaign

// Cancel before it starts sending
await sendr.campaigns.cancel(campaign.id);

You cannot cancel a campaign once it has started sending.

Plan limits summary

Feature	Free	Pro	Business	Enterprise
Monthly emails	3,000	50,000	200,000	Unlimited
Marketing emails/month	0	10,000	50,000	Unlimited
Campaigns	3	25	Unlimited	Unlimited
Audiences	3	25	Unlimited	Unlimited
Contacts	500	10,000	100,000	Unlimited

Free plan does not support marketing emails or campaigns. Upgrade to Pro or higher.

Deliverability tips for bulk sends

1. Warm up new domains gradually — start with a few hundred emails/day and increase over 2 weeks
2. Verify your audience — remove hard bounces and inactive addresses before large sends
3. Use suppression lists — Sendr automatically suppresses hard bounces; check your suppression list before importing
4. Segment your audience — engaged subscribers have higher open rates, which improves sender reputation
5. Include a real unsubscribe link — required by CAN-SPAM and GDPR, improves deliverability
6. Send at consistent times — ISPs look for consistent patterns from legitimate senders