Migrate from Postmark

Step-by-step guide to moving from Postmark to Sendbound. API mapping, message stream mapping, template porting, and webhook translation.

This guide covers everything specific to migrating from ActiveCampaign Postmark.

Before starting, read the general migration guide for the parallel-run strategy and DNS playbook.

What's different

	Postmark	Sendbound
API base	`https://api.postmarkapp.com`	`https://api.sendbound.com/v1`
Auth header	`X-Postmark-Server-Token: xxx`	`Authorization: Bearer sk_live_xxx`
Send endpoint	`POST /email`	`POST /send`
Template syntax	Mustache `{{variable}}`	Handlebars `{{variable}}` ✓ Compatible
Message streams	Outbound / Broadcasts	Transactional send / Campaigns
Template call	`POST /email/withTemplate`	`POST /send` with `templateId`
Bounce types	`HardBounce`, `SoftBounce`, etc.	`bounced` with `reason` string

Export from Postmark

Export templates via API

Postmark has no UI bulk export. Use their API:

# List all templates
curl -H "X-Postmark-Server-Token: YOUR_SERVER_TOKEN" \
  https://api.postmarkapp.com/templates

# Fetch individual template
curl -H "X-Postmark-Server-Token: YOUR_SERVER_TOKEN" \
  https://api.postmarkapp.com/templates/TEMPLATE_ID

The response includes HtmlBody and TextBody fields — save these as HTML files.

Export suppression list

curl -H "X-Postmark-Server-Token: YOUR_SERVER_TOKEN" \
  "https://api.postmarkapp.com/suppressions/dump?MessageStream=outbound" \
  > suppressions.csv

Export contacts

Postmark doesn't have a contact database for Broadcasts users built in. Export your subscriber list from your own database or from the Broadcasts UI if available.

Note webhook (delivery webhook) configuration

Server Settings → Webhooks tab — note which events are enabled and the endpoint URL for each stream.

Message stream mapping

Postmark separates transactional (Outbound stream) and broadcast (Broadcasts stream) email. Sendbound handles both:

Postmark stream	Sendbound equivalent
Outbound (transactional)	`POST /v1/send`
Broadcasts	Campaigns

API migration

Sending a transactional email

import * as postmark from 'postmark';

const client = new postmark.ServerClient(process.env.POSTMARK_SERVER_TOKEN!);

await client.sendEmail({
  From: 'hello@yourdomain.com',
  To: 'user@example.com',
  Subject: 'Welcome',
  HtmlBody: '<p>Welcome aboard!</p>',
  MessageStream: 'outbound',
});

await fetch('https://api.sendbound.com/v1/send', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.SENDBOUND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    to: 'user@example.com',
    from: 'hello@yourdomain.com',
    subject: 'Welcome',
    html: '<p>Welcome aboard!</p>',
  }),
});

Using a stored template

await client.sendEmailWithTemplate({
  From: 'hello@yourdomain.com',
  To: 'user@example.com',
  TemplateAlias: 'welcome',
  TemplateModel: {
    product_name: 'Acme',
    user_name: 'Jane',
    action_url: 'https://app.example.com/confirm/xyz',
  },
  MessageStream: 'outbound',
});

await fetch('https://api.sendbound.com/v1/send', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.SENDBOUND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    to: 'user@example.com',
    from: 'hello@yourdomain.com',
    templateId: 'tmpl_your_id',
    variables: {
      product_name: 'Acme',
      user_name: 'Jane',
      action_url: 'https://app.example.com/confirm/xyz',
    },
  }),
});

Template migration

Postmark uses Mustache ({{variable}}). Sendbound uses Handlebars which is a superset — all Mustache templates work unchanged.

Postmark	Sendbound	Notes
`{{variable}}`	`{{variable}}`	✓ No change
`{{#if condition}}`	`{{#if condition}}`	✓ No change
`{{{html_variable}}}`	`{{{html_variable}}}`	✓ Triple braces for unescaped HTML work
`{{product.url}}` (Postmark's action block)	Inline anchor tag	Replace action blocks with plain HTML buttons

Postmark's "Action" layout blocks (buttons, call-to-action sections) are proprietary template components. Export the rendered HTML from Postmark's template preview and import that directly — you get the same visual output without the proprietary syntax.

Webhook migration

Event name mapping

Postmark event	Sendbound event
`Delivery`	`email.delivered`
`Open`	`email.opened`
`Click`	`email.clicked`
`Bounce` (HardBounce)	`email.bounced`
`Bounce` (SoftBounce)	`email.bounced` (with `reason`)
`SpamComplaint`	`email.complained`
`SubscriptionChange`	`email.unsubscribed`

Signature verification

// Postmark uses a shared secret in the header
// but does not sign the payload body
const webhookSecret = process.env.POSTMARK_WEBHOOK_TOKEN;
if (req.headers['x-postmark-webhook-token'] !== webhookSecret) {
  return res.status(401).send('Unauthorized');
}

import crypto from 'crypto';

function verifyWebhook(payload: string, signature: string, secret: string) {
  const expected = crypto.createHmac('sha256', secret).update(payload).digest('hex');
  return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
}

const isValid = verifyWebhook(
  rawBody,
  req.headers['x-sendbound-signature'] as string,
  process.env.SENDBOUND_WEBHOOK_SECRET!,
);
if (!isValid) return res.status(401).send('Unauthorized');

Checklist

Migrate from Mailgun

Step-by-step guide to moving from Sinch Mailgun to Sendbound. API mapping, domain configuration, webhook translation, and parallel-run strategy.

Migrate from AWS SES

Step-by-step guide to moving from Amazon Simple Email Service (SES) to Sendbound. SDK replacement, IAM cleanup, SNS notification migration, and SMTP relay removal.

What's different Export from Postmark Export templates via API Export suppression list Export contacts Note webhook (delivery webhook) configuration Message stream mapping API migration Sending a transactional email Using a stored template Template migration Webhook migration Event name mapping Signature verification Checklist

Migrate from Postmark

On this page