The SNDR alternative to Postmark.

Postmark earned its reputation by treating transactional email as a separate craft from marketing — and we’ve learned a lot from how they think about reputation. SNDR is built in the same spirit. The difference is in the operational layer: a multi-MTA pool that fails over automatically, a webhook subsystem you can replay from the admin, and a Merchant-of-Record billing flow that handles VAT and sales tax for you. If you like Postmark’s philosophy but need an operator console and predictable global billing, this page is for you.

Drawn from public documentation and pricing as of build time. We try to keep this fair — file an issue if anything is wrong.

1. 1

   Install the SDK

   Add @rkiza/sndr alongside the postmark package — they coexist while you cut over.

   pnpm add @rkiza/sndr

2. 2

   Replace the send call

   Postmark’s sendEmail maps cleanly. Templates work too — create them in the SNDR dashboard or via the API.

   // before
   import postmark from 'postmark';
   const client = new postmark.ServerClient(process.env.POSTMARK_SERVER_TOKEN!);
   await client.sendEmail({ From: 'me@you.com', To: 'a@b.com', Subject: 'hi', HtmlBody: '<p>hi</p>' });
   
   // after
   import { Sndr } from '@rkiza/sndr';
   const sndr = new Sndr(process.env.SNDR_API_KEY!);
   await sndr.emails.send({ from: 'me@you.com', to: 'a@b.com', subject: 'hi', html: '<p>hi</p>' });

3. 3

   Migrate webhook handlers

   Postmark webhooks ship POSTed JSON. Swap to verifyWebhookSignature() and the typed event shape.

   import { verifyWebhookSignature } from '@rkiza/sndr';
   
   app.post('/webhooks/sndr', express.raw({ type: 'application/json' }), (req, res) => {
     if (!verifyWebhookSignature(req.body, req.header('x-sndr-signature') ?? '', process.env.SNDR_WEBHOOK_SECRET!)) {
       return res.status(400).send('bad signature');
     }
     // event.type: email.delivered | email.bounced | email.complained | email.unsubscribed
     res.status(200).send('ok');
   });

4. 4

   Reuse your DNS

   SPF and DMARC are reusable across providers. Add the SNDR include in the SPF "include:" chain. Generate a fresh DKIM selector for the SNDR sending domain.

5. 5

   Shadow traffic for a week

   Send a percentage of transactional emails through SNDR via a feature flag. Watch per-recipient-domain inbox rate match Postmark. Cut over fully when the curves are within a percentage point.