Resend 403 on first send: the from address must belong to a verified domain

TL;DR

Sending to anyone else gets a 403 telling you to verify a domain and change the from address. Doing this after the code is written turns a two-minute setup step into a debugging session. - When a send 403s, read the error: test-address-to-stranger vs unverified domain are different fixes.

Steps

1. Two knowledge-base pages cover this, and together they explain almost every

first-send 403:

2. The test address only sends to yourself. Emails from the default test address can only go to your own email address. Sending to anyone else gets a 403 telling you to verify a domain and change the from address.

3. Any other from domain must be verified. If the domain in your from address does not match a verified domain on your account, the API returns a 403 domain-mismatch error.

4. • Before writing any send code, verify the domain in the dashboard and set the

   from address to an address on it. Doing this after the code is written turns a two-minute setup step into a debugging session.

• When a send 403s, read the error: test-address-to-stranger vs unverified domain are different fixes. The error text names which one.

• The to address matters too during testing: with the test from address, keep recipients to your own address until the domain is verified.

• Deliverability starts here as well: a verified domain with proper DNS is what keeps the email out of spam.

When to use

You are seeing this: Two knowledge-base pages cover this, and together they explain almost every first-send 403: 1. Use this skill when you run into "Resend 403 on first send: the from address must belong to a verified domain".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Resend's knowledge base documents the test-address recipient restriction and the verified-domain requirement behind first-send 403s. Verified live at https://resend.com/docs/knowledge-base/403-error-resend-dev-domain and https://resend.com/docs/knowledge-base/403-error-domain-mismatch.