Migrate from Resend

Coming from Resend, you will recognize almost everything: the send body, the batch of 100, the Idempotency-Key, scheduling with cancel and signed webhooks. The differences are in the details below. Follow the safe migration order and use this guide to translate each part.

The send call#

curl https://api.resend.com/emails \
  -H "Authorization: Bearer $RESEND_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "Shop <orders@example.com>",
    "to": ["ana@example.com"],
    "subject": "Order 1042 confirmed",
    "html": "<p>Thanks, Ana!</p>",
    "tags": [{ "name": "category", "value": "order" }]
  }'

curl https://api.couryo.com/v1/emails \
  -H "Authorization: Bearer $COURYO_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: order-1042-confirmation" \
  -d '{
    "from": "Shop <orders@example.com>",
    "to": ["ana@example.com"],
    "subject": "Order 1042 confirmed",
    "html": "<p>Thanks, Ana!</p>",
    "text": "Thanks, Ana!",
    "tags": { "category": "order" }
  }'

Resend answers { "id": "..." }; Couryo answers 202 { "id": "msg_...", "status": "queued" }, only after the email is in the queue.

Fields#

React Email#

Couryo takes ready HTML. With React Email, render it first:

import { render } from "@react-email/render";
import { OrderConfirmed } from "./emails/order-confirmed";

const html = await render(<OrderConfirmed name="Ana" />);
const text = await render(<OrderConfirmed name="Ana" />, { plainText: true });

await fetch("https://api.couryo.com/v1/emails", {
  method: "POST",
  headers: { Authorization: `Bearer ${process.env.COURYO_API_KEY}`, "Content-Type": "application/json", "Idempotency-Key": "order-1042" },
  body: JSON.stringify({ from: "Shop <orders@example.com>", to: "ana@example.com", subject: "Order 1042 confirmed", html, text }),
});

For emails your team edits without a deploy, create saved templates or use the visual editor and send template with variables.

Events and webhooks#

Both sign following Standard Webhooks: Couryo uses the webhook-id, webhook-timestamp and webhook-signature headers (HMAC-SHA256 with the whsec_... secret). If your receiver checks the signature with a library of the standard, change the secret and the header prefix. The body type comes without the email. prefix (for example, "type": "bounced") and data brings email_id, recipient, the SMTP code, the raw answer of the receiving server and the plain-language explanation, in the account language (webhooks).

Audiences, contacts and topics#

• Export each audience as CSV and import into Couryo, with the consent confirmation. Whoever had unsubscribed: add them as marketing suppressions first (copy the suppressions).
• Resend topics exist at Couryo with the same name: create them under Contacts > Topics or with POST /v1/topics. The marketing footer leads to the preferences page.
• Broadcasts become campaigns, with an audience by tag, attribute or topic.

DNS#

Resend publishes the DKIM key on its own record (resend._domainkey) and the return path on the send subdomain. None of them conflicts with Couryo's (couryo1._domainkey, couryo2._domainkey and bounces), so both stay published during the migration.

1. Publish Couryo's records and wait for the domain to be verified.
2. Keep the DMARC record you already have; to get the reports in the deliverability agent, add mailto:reports@dmarc.couryo.com to rua.
3. Once all traffic is on Couryo and 7 days have passed, delete resend._domainkey and the records of the send subdomain. Do not touch the MX or the SPF of your mailboxes.