Send emails with SMTP
Prerequisites
Section titled “Prerequisites”Before you start, you'll need:
- A Resend API key
- A verified domain
Prefer watching a video? Check out our video walkthrough below.
SMTP Settings
Section titled “SMTP Settings”When configuring your SMTP integration, use the following settings:
- Host:
smtp.resend.com - Port:
25,465,587,2465, or2587 - Username:
resend - Password:
YOUR_API_KEY
Ports help to instruct the type of security you want to use in your SMTP connection.
| Type | Port | Security |
|---|---|---|
| SMTPS | 465, 2465 |
Implicit SSL/TLS (Immediately connects via SSL/TLS) |
| STARTTLS | 25, 587, 2587 |
Explicit SSL/TLS (First connects via plaintext, then upgrades to SSL/TLS) |
Idempotency Key
Section titled “Idempotency Key”Idempotency keys are used to prevent duplicate emails. You can add the Resend-Idempotency-Key header to your emails sent with SMTP to prevent duplicate emails.
From: Acme <onboarding@resend.dev>To: delivered@resend.devSubject: hello worldResend-Idempotency-Key: welcome-user/123456789<p>it works!</p>Learn more about idempotency keys.
Custom Headers
Section titled “Custom Headers”If your SMTP client supports it, you can add custom headers to your emails.
Here are some common use cases for custom headers:
- Prevent threading on Gmail with the
X-Entity-Ref-IDheader - Include a shortcut for users to unsubscribe with the
List-Unsubscribeheader
Once configured, you can start sending emails via SMTP. Below are some frequently asked questions:
What if I need logs from the server to debug?
We currently don't provide SMTP server logs for debugging. If you run into issues, please reach out to support.
Where do I see the emails sent with SMTP?
Emails sent with SMTP will show in your emails table.
Does the rate limit apply when sending with SMTP?
Yes, the rate limit is the same as the API.