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

# Send emails with SMTP

> Send through the Apollo Signal SMTP relay

Use this guide to send one server-side transactional email and confirm its lifecycle in Apollo Signal.

<Note>
  Replace every `mail.company.com` example with a domain that is verified in your project.
</Note>

<Steps>
  <Step title="Create a sending key">
    Open **API keys** in Apollo Signal. Create a key with **Emails: Send** permission, copy it once, and store it in a server-side secret.
  </Step>

  <Step title="Verify the From domain">
    Open **Domains**, add the sending domain, publish the required DNS records, and wait for the domain to show as verified.
  </Step>

  <Step title="Copy your SMTP settings">
    Open **Settings → SMTP** in Apollo Signal and copy the host shown for your project.
    Create an API key with `emails:send` and use it as the SMTP password.
  </Step>

  <Step title="Send the message">
    ```ini theme={"dark"}
    Host=YOUR_SIGNAL_SMTP_HOST
    Port=587
    Security=STARTTLS
    Username=apikey
    Password=ap_signal_...

    From=auth@mail.company.com
    To=alex@example.com
    Subject=Reset your password
    ```
  </Step>
</Steps>

## Required values

| Value   | Requirement                                                                                                                                      |
| ------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| API key | Must belong to the active project and include `emails:send`. REST requests use `Authorization: Bearer <key>`. SMTP uses the key as the password. |
| From    | Must use a verified sending domain in the same project. A display name is optional.                                                              |
| To      | Must be a valid recipient address for this first send. Keep recipient input on the server and validate it before use.                            |
| Content | Include a non-empty subject and at least one of `html` or `text`.                                                                                |

## Confirm acceptance

Your SMTP client should receive a successful SMTP reply after Apollo Signal accepts the message.
Acceptance means Signal queued the message. It does not mean the recipient server delivered it.
Open **Emails** to follow the message through delivery, bounce, complaint, or failure.

## Check the message

Open **Emails** and select the message. Check its current status, recipient, timestamps, provider response, content preview, and event timeline.
Delivery events are asynchronous, so do not treat the initial API or SMTP acceptance as final delivery.

## Common failures

| Symptom                    | What to check                                                                                         |
| -------------------------- | ----------------------------------------------------------------------------------------------------- |
| `401 Unauthorized`         | The key is missing, malformed, expired, or no longer active.                                          |
| `403 Forbidden`            | The key does not include `emails:send` or belongs to another project.                                 |
| Validation error           | The From domain is unverified, the recipient is invalid, or both `html` and `text` are missing.       |
| `429 Too Many Requests`    | Slow down, respect the response headers, and retry with backoff.                                      |
| Accepted but not delivered | Open the email timeline and check for bounce, complaint, suppression, rejection, or provider failure. |

## Production checklist

* Keep the API key in a secret manager.
* Use a restricted key dedicated to this service.
* Add an `idempotencyKey` when your job runner can retry the same logical send.
* Configure signed webhooks for final delivery outcomes.
* Monitor bounce, complaint, suppression, and quota signals in the dashboard.

<CardGroup cols={2}>
  <Card title="Email API" icon="code" href="/api-reference/emails/send-email">
    Review every send field and response.
  </Card>

  <Card title="Manage emails" icon="envelope" href="/signal/dashboard/emails/introduction">
    Learn the statuses and troubleshooting workflow.
  </Card>
</CardGroup>