Sendbound API Reference

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.

ℹ

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 `template`
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',
});

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',
});

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

ℹ

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');
}

Migrate from Postmark