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Target vendor: Resend API. Webhook signing: Svix-style HMAC-SHA256 (svix-id, svix-timestamp, svix-signature headers).

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Mirror URL

https://resend-<session_id>.mirra.run
Example: https://resend-a7k2.mirra.run.

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SDK compatibility

Official Resend SDKs work against the mirror with zero code changes when routed via the TLS proxy: 
import { Resend } from 'resend';

const resend = new Resend(process.env.RESEND_API_KEY);

const { id } = await resend.emails.send({
  from: 'hello@mail.acme.com',
  to: 'alice@test.com',
  subject: 'Welcome',
  html: '<p>Welcome to Acme.</p>',
});
// → routed to resend-a7k2.mirra.run

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Supported surface

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Resources

Send single emails, batch-send, retrieve by ID, list. HTML + plain text bodies, attachments, tags, reply-to, cc/bcc.
Create, verify, retrieve, list, delete. Verification status transitions (pending → verified / failed). DNS record generation.
Create, list, revoke. Name, scope, permission levels. Last-used tracking.
Audience CRUD. Contact add, update, unsubscribe, delete. Bulk import.
Create, schedule, send, list. Audience targeting. Preview.

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Webhooks

All Resend webhook event types fire with vendor-correct Svix-style signatures:
  • email.sent — immediately after a successful send
  • email.delivered — a few seconds after send (configurable per fixture)
  • email.delivery_delayed — when delivery is delayed by downstream providers
  • email.bounced — hard and soft bounces
  • email.complained — spam complaints
  • email.opened — tracking pixel hit
  • email.clicked — link click
Signing headers: 
svix-id:        msg_28pxRt9jRYvJMq8yc6ZD
svix-timestamp: 1713802534
svix-signature: v1,g0hM9SsE+OTPJTGt/tmIKtSyZlE3uFJELVlNIOLJ1OE=
Verify using the official Resend webhooks library, no code changes: 
import { Webhook } from 'svix';

const wh = new Webhook(process.env.RESEND_WEBHOOK_SECRET);
const event = wh.verify(rawBody, {
  'svix-id':        req.headers['svix-id'],
  'svix-timestamp': req.headers['svix-timestamp'],
  'svix-signature': req.headers['svix-signature'],
});

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Built-in fixtures

No domains, no emails. A blank Resend account.
One verified domain mail.acme.com, 100 sent emails across the last 7 days with realistic delivery/bounce/open rates. Good for testing scale behavior.
Domain with recent bounce rate above the provider’s threshold — suspended state. Good for testing your handler’s response to email.bounced and domain suspension.
Audience with 1,000 contacts and three prior broadcasts. Good for testing broadcast flows.
Account at monthly send limit. Any POST /emails returns 429 with Resend’s exact rate-limit payload. Good for testing your quota-exceeded handling.
Load a fixture: 
mirra up --mirrors=resend --seed=resend:transactional-busy

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Coverage gaps

  • Suppression lists — not yet mirrored.
  • Custom domains with CNAME proxies — mocked as always-valid.
  • Open/click tracking pixels — simulated via /_mirra/simulate, not from real client requests.
See status.mirra.run/resend for the live list.

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Simulating events

Real delivery timing (a few seconds between email.sent and email.delivered) is simulated by the engine’s event-dispatch scheduler — you get realistic timing without waiting on actual SMTP. To force an immediate bounce or complaint for testing: 
curl -X POST https://resend-a7k2.mirra.run/_mirra/simulate \
  -H "Content-Type: application/json" \
  -d '{ "event": "email.bounced", "emailId": "email_abc", "bounce": { "type": "hard", "reason": "user not found" } }'
See API reference for the full event list.

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Where to go next

Twilio

The SMS mirror.

Stripe

The payments mirror.

First scenario

Write and run a Resend scenario end-to-end.