How to Set Up and Send Emails in Auth0 Using SendLayer

What Is Auth0’s Built-In Email Provider, and Why Isn’t It Enough?

Auth0’s built-in provider works automatically when you first create a tenant. You don’t configure anything; verification and password reset emails just work out of the box.

But it has hard limits you can’t override:

• Sends from [email protected] (not your domain)
• Capped at 10 emails per minute
• No custom email templates
• Not supported for production use

These limits are by design. Auth0 expects you to connect a real email provider for any live app. The setup takes a few minutes and gives you full control over delivery and branding.

What Do You Need Before You Configure Email in Auth0?

You’ll need a verified sending domain and SMTP credentials from SendLayer before you start. Here’s a full checklist.

Prerequisites

• An Auth0 account (free tier works fine)
• A SendLayer account with a verified sending domain
• SPF and DKIM records published for your sending domain
• Admin access to your Auth0 dashboard

How Do You Set Up a Custom Email Provider in Your Auth0 Email Account?

You set up a custom SMTP provider like SendLayer as your Auth0 provider by entering your SMTP credentials under Branding » Email Provider. Here’s how to do it in 4 steps.

Step 1: Get Your SendLayer SMTP Credentials

Log in to SendLayer and go to Settings » SMTP Credentials.

You’ll see the following credentials:

Copy these values. You’ll paste them into Auth0 in the next step.

Step 2: Enable a Custom Email Provider in Auth0

Now, let’s configure the email provider settings in Auth0. Start by logging in to your Auth0 dashboard.

Once you’re logged in, navigate to Branding » Email Provider.

Then toggle on the Use my own email provider option.

Next, select SMTP Provider from the provider list.

Step 3: Enter Your SendLayer SMTP Settings

After that, additional fields will appear. You’ll need to fill out the SMTP form with your SendLayer details:

Once you’re done entering the details, click Save.

Step 4: Send a Test Email in Auth0

After saving your email configuration, scroll to the bottom of the Email Provider page and click Send Test Email.

If it worked, you’ll get a confirmation email from your verified domain.

If you don’t, go to Monitoring » Logs in Auth0 to check for errors.

How Do You Customize Auth0 Email Templates?

Auth0 email templates let you control the content of every email it sends, from account verification to password resets.

To customize your email templates, go to Branding » Email Templates and choose the template you want to edit.

Each template uses Liquid syntax to dynamically pull in user and app data. You can find the full list of template types in the Auth0 email templates docs. For ideas on what to include, see our guide to password reset email best practices.

What Variables Can You Use in Auth0 Email Templates?

Here are the most useful built-in variables:

How Do You Send Custom Emails with Auth0 Actions?

Auth0 Actions let you trigger emails that aren’t part of the standard auth flow. You can send a welcome email on signup, a login alert, or any custom notification your app needs. If you need inspiration, our collection of welcome email examples is a good starting point.

Example: Trigger a Welcome Email After Signup

This example uses the Post User Registration trigger to send a welcome email via the SendLayer API.

In your Auth0 dashboard, go to Actions » Triggers. Once there, select the post-user-registration trigger.

Next, click the Create Action button to configure a new action.

In the overlay that appears, you’ll need to enter a name for the custom action. This name is for internal purposes only.

For this example, I’ve named it “Send Welcome Email”. After that, choose the Post User Registration trigger.

Once done, click Create to proceed.

You’ll be directed to a code editor. Go ahead and paste the code below into the custom snippet editor:

const https = require("https");

exports.onExecutePostUserRegistration = async (event) => {
  const payload = JSON.stringify({
    From: { email: process.env.SENDLAYER_FROM, name: "Your App" },
    To: [{ email: event.user.email, name: event.user.name || "" }],
    Subject: "Welcome to Your App",
    ContentType: "HTML",
    HTMLContent: `<p>Hi ${event.user.name || "there"}, welcome aboard!</p>`,
  });

  await new Promise((resolve, reject) => {
    const req = https.request(
      {
        hostname: "console.sendlayer.com",
        path: "/api/v1/email",
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          Authorization: `Bearer ${process.env.SENDLAYER_API_KEY}`,
          "Content-Length": Buffer.byteLength(payload),
        },
      },
      (res) => {
        res.on("data", () => {});
        res.on("end", resolve);
      }
    );
    req.on("error", reject);
    req.write(payload);
    req.end();
  });
};

The snippet above connects to the SendLayer email API and dynamically adds the user’s email and name to the request parameter.

Notice that we reference the sender email and API key from an environment variable. It is good practice to use environment variable to manage sensitive credentials.

Now, I’ll need to add the environment variables. To do so, click Add Secret.

In the overlay that appears, set the environment variable Key as SENDLAYER_API_KEY. Then paste your API key into the Value field and click Create.

Repeat the same process and add the SENDLAYER_FROM value. This is the sender email address and should use the domain you verified in your SendLayer account.

To retrieve your API key, log in to your SendLayer account area and navigate to Settings » API Keys.

After adding the environment variables and configuring the action, click Deploy to publish it.

For a full walkthrough of password reset flows, see how to implement password reset in Node.js.

How Do You Troubleshoot Email Delivery in Auth0?

If emails aren’t arriving, work through these checks in order. In my experience, mismatched SMTP credentials cause more than half of all delivery failures.

Check Auth0 Logs

Go to Monitoring » Logs in Auth0. Filter for failed events. Look for type fs (failed send email) for error details.

Verify your SendLayer credentials

Re-check your API key and username in Settings » SMTP Credentials in SendLayer. Re-enter them in Auth0 to rule out typos.

Confirm SPF and DKIM records

Use a tool like MXToolbox to check your domain’s DNS records. Auth0 email delivery depends on these passing. For a deeper look at email authentication records, read our guide to improving email security.

Check SendLayer delivery logs

In SendLayer, go to the Logs section. You’ll see whether SendLayer received the request from Auth0 and the result.

Check IP allowlisting

Some SMTP setups require you to allowlist Auth0’s outbound IPs. Go to Branding » Email Provider in Auth0. You’ll see a list of the required IP addresses there.

FAQs – Send Email in Auth0

Below, we’ve answered some of the top questions developers ask about setting up and sending emails in Auth0.