The SNDR alternative to Mailgun.

Mailgun pioneered transactional email infrastructure for developers and has continued to scale through the Sinch acquisition. SNDR's bet is on operational density — a single typed SDK, idempotent send by default, signed webhooks with retries and a replay button, and per-MTA delivery curves visible in the dashboard the moment something starts misbehaving. If you've outgrown Mailgun's UI or want a tighter feedback loop between production and your on-call engineer, this is the page 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 mailgun.js — they coexist while you cut over.

   pnpm add @rkiza/sndr

2. 2

   Replace the send call

   Mailgun’s messages.create() maps directly. Headers become a typed object; tags become structured key/value pairs for filterable analytics.

   // before
   import formData from 'form-data';
   import Mailgun from 'mailgun.js';
   const mg = new Mailgun(formData).client({ username: 'api', key: process.env.MAILGUN_API_KEY! });
   await mg.messages.create('mg.yourdomain.com', {
     from: 'me@yourdomain.com', to: 'a@b.com', subject: 'hi', html: '<p>hi</p>',
   });
   
   // after
   import { Sndr } from '@rkiza/sndr';
   const sndr = new Sndr(process.env.SNDR_API_KEY!);
   await sndr.emails.send({
     from: 'me@yourdomain.com', to: 'a@b.com', subject: 'hi', html: '<p>hi</p>',
   });

3. 3

   Migrate webhook handlers

   Mailgun posts form-encoded data; SNDR posts JSON. Verify with the shipped helper and switch your handler to the discriminated-union 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');
     }
     const event = JSON.parse(req.body.toString('utf8'));
     switch (event.type) {
       case 'email.delivered': /* event.data.email_id, event.data.to */ break;
       case 'email.bounced':   /* event.data.email_id, event.data.error */ break;
       case 'email.unsubscribed': /* event.data.addresses */ break;
     }
     res.status(200).send('ok');
   });

4. 4

   Reuse your DNS

   SPF can keep both providers’ include: directives during cutover. Add a fresh DKIM CNAME or TXT for the SNDR sending domain — Mailgun’s key stays put.

5. 5

   Shadow + cut over

   Roll a percentage of sends through SNDR via a feature flag. When per-recipient-domain inbox rate matches Mailgun on the dashboard, flip the rest. Most teams complete the move in under a week.