Resend

Overview

Resend is a modern email API that makes it easy to send transactional and marketing emails from your Emergent app. With its developer-friendly interface and reliable delivery, Resend is ideal for password resets, welcome emails, notifications, and more.

This guide walks you through integrating Resend into your Emergent project so your AI agents can send emails on behalf of your application.

Using Resend with Emergent

You can use Resend in two ways:

Automatically with Emergent's Universal LLM Key - recommended.
With your own Resend API key - if you prefer to use your own Resend account and credentials.

Using Resend with Universal LLM Key

The preferred approach is to use Resend through Emergent's Universal LLM Key.

Describe the email functionality you want in your Emergent project, such as:

"Send a confirmation email when a user submits the contact form."

Emergent will configure Resend and handle the required credentials for your application.

Once connected, you can specify the email flows you want your application to support, such as password resets, welcome emails, or notifications.

Connecting Your Own Resend API Key

If you want to use your own Resend API key, you can provide your key when Emergent asks for your Resend credentials.

Log in to Resend

Go to Resend and log in or create an account.

Open API Keys

Go directly to the Resend API Keys page.

Open the Resend dashboard.
Go to API Keys.

Create the API Key

Click Create API Key.
Give the API key a name so you can identify which app it is for.
- Example:
```
Customer Feedback App
```
Create the API key.

Copy the API Key

Copy the complete secret API key immediately.

It will look like:

re_...

Connect Resend to Emergent

When Emergent asks for your Resend credentials, provide the API key
Agent will securely configure the key and connect Resend to your application.

Verify Your Domain

For testing, you can start with your available verified sender setup.
To send emails to real customers, go to Domains → Add Domain in Resend.
Enter a domain that you own.
Add the DNS records provided by Resend to your domain provider.

Once connected, test your email flow to confirm that messages are being sent and delivered correctly.

Common use cases

User onboarding

Welcome emails, email verification links, and getting-started guides sent automatically when users sign up.

Transactional alerts

Order confirmations, shipping updates, payment receipts, and account security notifications.

Scheduled digests

Daily or weekly summaries, activity reports, and content recommendations sent on a schedule.

Team collaboration

Invitations, mentions, comment notifications, and shared document alerts within your app.

Best practices

Verify your domain for production use - emails from verified domains have better deliverability and avoid sandbox limits.
Use environment variables for API keys and never commit them to your codebase.
Handle errors gracefully - ask the agent to retry failed sends or log them for manual review.
Personalize emails - include the recipient's name and relevant context to improve engagement.
Monitor bounce rates - if Resend reports high bounces, check your recipient list quality and unsubscribe flow.

Warning

Resend enforces rate limits based on your plan tier. If you're sending high volumes, coordinate with the agent to implement queueing or batch sending to stay within limits.

Troubleshooting

Issue	Solution
"Invalid API key" error	Double-check the `RESEND_API_KEY` variable value in your Emergent project. Regenerate the key in Resend if needed.
Emails not arriving	Check your spam folder. Verify your sending domain in the Resend dashboard. Review Resend's Logs for delivery errors.
Rate limit exceeded	Ask the agent to add retry logic with exponential backoff, or upgrade your Resend plan for higher limits.
"From" address rejected	Ensure the sender address matches your verified domain. Sandbox emails must use `onboarding@resend.dev` .