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Move the integration in stages: inventory what your application sends through SES, prepare a verified sending domain and API key in Resend, replace the send call, then rebuild event handling and verify production behavior. A successful API response means a provider accepted a request; it does not by itself establish inbox delivery. There is no established one-to-one SES-to-Resend converter or complete field mapping, so preserve the behavior your application actually depends on.
1. Inventory your SES setup and message behavior
Before changing code, find every SES send call and record what each one sends. Include password resets, receipts, alerts, templates, and less common messages such as administrative notifications. The migration is not complete if one code path still sends through SES unintentionally.
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- Record the AWS region, sending identities, and whether the account has production access or is still subject to sandbox restrictions. SES setup includes verified identities and production-access requirements; see AWS’s production-access documentation.
- Identify whether the application sends through the SES API or SMTP. If it uses SMTP, record the region-specific SMTP credentials and where they are stored.
- For every message type, note the sender, recipients, reply-to, CC/BCC, subject, text and HTML bodies, templates, attachments, headers, tags, and any configuration-set behavior.
- Record the event destinations, dashboards, alerts, and internal status values used for delivery, bounce, and complaint monitoring.
SES identity verification and domain-authentication considerations are described in AWS’s identity documentation. Do not assume that the SES setup itself transfers when you change providers.
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Create a Resend API key and verify the sending domain you intend to use in the from field. The Resend Node.js guide shows an API-key client and a verified-domain sender: Send emails with Node.js. Configure the key through your environment or secret-management system, not in source control; any sample key shown in documentation is illustrative.
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Check your DNS and sender authorization before routing production messages. Test with an address on the verified domain, and keep the old SES configuration available during rollout so the change can be reversed without reconstructing credentials.
3. Replace the Node.js send call
The reviewed AWS example uses the older AWS SDK for JavaScript v2 pattern, AWS.SES().sendEmail(params).promise(). That is not AWS SDK v3 syntax. Check which SDK version your application actually installs before modifying or removing its SES code; the cited example is at AWS SDK for JavaScript v2 SES examples.
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Resend’s documented Node.js pattern creates a client with the API key and calls resend.emails.send():
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import { Resend } from 'resend';
const resend = new Resend(process.env.RESEND_API_KEY);
const { data, error } = await resend.emails.send({
from: 'Acme <[email protected]>',
to: ['[email protected]'],
subject: 'Example',
html: '<p>Example message</p>',
});
if (error) {
// Handle or log the provider error without exposing secrets or message contents.
} else {
// Persist the returned provider identifier if your application needs it.
}Adapt this shape to the installed Resend SDK version and your application’s architecture. Handle the returned error explicitly, and decide whether and how to persist the provider identifier. Avoid logging API keys or sensitive message contents.
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Map only the features your application uses
Do not translate an SES parameter list mechanically. Compare each actual message path with the Resend API and confirm support for the fields and behaviors you rely on. Resend’s send guide documents its request pattern, but the reviewed vendor pages do not provide a complete SES-to-Resend field-by-field conversion table. Treat these as migration checks, not assumptions of parity:
- Addresses: sender, recipient lists, reply-to, CC, and BCC.
- Content: subject, plain-text and HTML versions, templates, and any dynamic data or rendering performed by your application.
- Extras: attachments, custom headers, tags, and SES configuration-set functions.
- Application behavior: how errors are surfaced, whether sends are retried, and how provider IDs connect to logs or records.
4. Rebuild event handling and operational states
A send request accepted by a provider is not proof that the message reached an inbox. SES describes acceptance with a message ID and later outcomes such as delivery, bounce, or complaint; see AWS’s sending-activity monitoring documentation. Keep these stages distinct in your application metrics and alerts.
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SES can publish event data through destinations such as Amazon SNS and Kinesis Data Firehose. Resend instead documents event webhooks and signing-secret verification. Review SES event publishing, Resend webhooks, and Resend webhook signature verification.
Implement the Resend webhook endpoint intentionally: verify incoming signatures, map Resend event names into stable internal states, and make processing safe against retries or duplicate events. Do not assume SES and Resend event payloads or names are interchangeable. Keep alerts meaningful after the change—for example, distinguish provider errors from later delivery failures rather than counting every accepted request as delivered.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.5. Test representative messages, then switch in stages
A staged rollout is a prudent operational approach; it is not a vendor-prescribed SES-to-Resend migration procedure. Start with test traffic, then move a limited production path or share of traffic if your architecture permits, while retaining a clear rollback route.
- Send a representative test for each distinct message type. Cover different templates or bodies, sender identities, recipient forms, and any attachments or special headers in use.
- Inspect the result. Check rendered content, links, sender details, headers, attachment handling, application error handling, and webhook processing.
- Move production traffic deliberately. Switch the selected code path or traffic share only after its setup and event flow work as expected.
- Monitor the full lifecycle. Watch accepted sends, delivery events, delays, bounces, complaints, webhook processing, and application errors. Compare equivalent message types and time windows rather than treating API acceptance as a delivery metric.
- Keep rollback actionable. Preserve the SES configuration and know how to restore its send path if the new integration or its event handling fails.
What this migration does—and does not—establish
The available provider documentation supports comparing setup requirements, API patterns, sender authentication, event plumbing, and the message features your application uses. It does not establish that Resend is cheaper, more reliable, or more deliverable than SES, nor does it establish a migration duration or direct feature parity. Make those decisions using current, comparable evidence for your own traffic and requirements rather than inferring a winner from integration examples.
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