Switching from Resend to Sendflit without rewriting your code

Quick answer

Switching from Resend to Sendflit is mainly a configuration change. Swap your API key, point your Resend SDK at Sendflit’s /resend endpoint, and keep the calls your application already makes.

Key takeaways

• Swap the API key and point your Resend SDK at Sendflit’s /resend endpoint.

• Batch sends, scheduled sends and webhooks keep the same call shapes.

• Verify every sending domain before the first production send.

What changes when you switch from Resend?

The change is mostly configuration. You swap the API key, point your SDK at Sendflit’s /resend endpoint, and keep the calls your application already makes. Batch sends, scheduled sends and webhooks run through the same code paths, so the logic around them does not need to be rewritten.

Before you change anything, list the sending domains, templates and suppressions your application depends on. Sendflit can import domains, contacts, templates and suppressions from Resend, so the new account starts from the same state your recipients expect.

How do you migrate safely?

Run the new key in staging first. Send a test message from a verified domain, check the delivery event, and confirm that your webhook receiver accepts the signed payload. Only then move production traffic.

Keep the old provider active until each sending domain shows a passing deliverability score. Every domain is scored out of 100, and every lost point comes with a named fix.

What are the common mistakes?

The most common mistake is changing the key without verifying the sending domain. Mail from an unverified domain is refused with a 403 response. The second is forgetting webhook endpoints, so update the URL that receives delivery events.

Check from addresses too. Every sender address must belong to a verified domain, so search your code for hard-coded addresses that still point at the old account.

Frequently asked questions

Do I need to rewrite my Resend code?

Usually not. For most applications you change the API key and point the SDK at Sendflit’s /resend endpoint. Batch sends, scheduled sends and webhooks keep their existing call shapes.

Can I import my Resend domains and contacts?

Yes. Sendflit can import domains, contacts, templates and suppressions from Resend.

What if my first send fails?

A 403 response usually means the sending domain is not verified. Check the domain status and its DNS records, then retry.

Last updated October 2026 by the Sendflit team.