> ## Documentation Index
> Fetch the complete documentation index at: https://resend.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Send emails using Customer.io with SMTP

> Learn how to integrate Customer.io with Resend SMTP.

### Prerequisites

Before you start, you'll need:

* A Resend [API key](/docs/create-an-api-key)
* A [verified domain](/docs/add-a-domain)

## Guide

**1. Get the Resend SMTP credentials**

When configuring your SMTP integration, you'll need to use the following credentials:

* **Host**: `smtp.resend.com`
* **Port**: `465`
* **Username**: `resend`
* **Password**: `YOUR_API_KEY`

**2. Integrate with Customer.io SMTP**

After logging into your [Customer.io](https://customer.io) account, you'll need to enable the SMTP integration.

1. Go to **Settings** > **Workspace Settings**.

![Customer.io SMTP - Workspace Settings](https://mintcdn.com/resend/ABWmVTZIHGIFNTFD/images/customer-io-smtp-1.png?fit=max\&auto=format\&n=ABWmVTZIHGIFNTFD\&q=85\&s=97d3402e7acb7c66e5d54ff2886dd4e3)

2. Go to the Messaging tab and select **Email**.

![Customer.io SMTP - Email](https://mintcdn.com/resend/ABWmVTZIHGIFNTFD/images/customer-io-smtp-2.png?fit=max\&auto=format\&n=ABWmVTZIHGIFNTFD\&q=85\&s=af35d8a9c99681e1a508694f02157943)

3. Select the **Custom SMTP** tab and click **Add Custom SMTP Server**.

![Customer.io SMTP - Add Custom SMTP Server](https://mintcdn.com/resend/ABWmVTZIHGIFNTFD/images/customer-io-smtp-3.png?fit=max\&auto=format\&n=ABWmVTZIHGIFNTFD\&q=85\&s=1d18082018463dc5989fb91d8f881b39)

4. Select **Other SMTP** and click **Continue to set up**.

![Customer.io SMTP - Other SMTP](https://mintcdn.com/resend/ABWmVTZIHGIFNTFD/images/customer-io-smtp-4.png?fit=max\&auto=format\&n=ABWmVTZIHGIFNTFD\&q=85\&s=acc404b8b5b7fc11db0279d84453cb11)

5. Copy-and-paste the SMTP credentials from Resend to Customer.io.

![Customer.io SMTP integration](https://mintcdn.com/resend/ABWmVTZIHGIFNTFD/images/customer-io-smtp-5.png?fit=max\&auto=format\&n=ABWmVTZIHGIFNTFD\&q=85\&s=519742fc4d97d06646fdd52de4f373fd)