# Send emails with SMTP

## Prerequisites

Before you start, you'll need:

- A Resend [API key](/guides/get-started-create-an-api-key)
- A [verified domain](/guides/get-started-add-a-domain)

Prefer watching a video? Check out our video walkthrough below.

[YouTube video player](https://www.youtube.com/watch?v=MM1JE6-inmc)

## SMTP Settings

When configuring your SMTP integration, use the following settings:

- **Host**: `smtp.resend.com`
- **Port**: `25`, `465`, `587`, `2465`, or `2587`
- **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

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.

```yaml SMTP {4} theme={"theme":{"light":"github-light","dark":"vesper"}}
From: Acme <onboarding@resend.dev>
To: delivered@resend.dev
Subject: hello world
Resend-Idempotency-Key: welcome-user/123456789

<p>it works!</p>
```

Learn more about [idempotency keys](/guides/learn-dashboard-emails-idempotency-keys).

## 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-ID` header
- Include a shortcut for users to unsubscribe with the `List-Unsubscribe` header

## FAQ

Once configured, you can start sending emails via SMTP. Below are some frequently asked questions:

::::accordion-group
:::accordion{title="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](https://resend.com/help).
:::

:::accordion{title="Where do I see the emails sent with SMTP?"}
Emails sent with SMTP will show in your [emails
table](https://resend.com/emails).
:::

:::accordion{title="Does the rate limit apply when sending with SMTP?"}
Yes, the rate limit is the [same as the
API](/guides/api-reference-introduction#rate-limit).
:::
::::

## Related pages

- [Send Auth0 transactional emails with Resend](./get-started-send-with-auth0.md)
- [Send emails using Customer.io with SMTP](./get-started-send-with-customer-io-smtp.md)
- [Send emails using Django with SMTP](./get-started-send-with-django-smtp.md)
- [Send emails using Laravel with SMTP](./get-started-send-with-laravel-smtp.md)
- [Send emails using Liferay with SMTP](./get-started-send-with-liferay-smtp.md)
- [Send emails using Nodemailer with SMTP](./get-started-send-with-nodemailer-smtp.md)
- [Send emails using PHPMailer with SMTP](./get-started-send-with-phpmailer-smtp.md)
- [Send emails using Rails with SMTP](./get-started-send-with-rails-smtp.md)
- [Send emails using Retool with SMTP](./get-started-send-with-retool-smtp.md)
- [Send emails using Supabase with SMTP](./get-started-send-with-supabase-smtp.md)

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