# Transactional Emails (/concepts/transactional-emails)

Transactional emails are emails sent directly through the API. They are typically used for one-to-one communication, such as password resets, order confirmations, and notifications.

## Sending with attachments

Plunk supports sending attachments with transactional emails. By default, you can include up to 10 attachments per email with a maximum total size of 10MB. Attachments should be base64 encoded and included in the `attachments` array when sending the email via the [/v1/send](/api-reference/public-api/sendEmail) endpoint.

The total message size cannot exceed 40 MB. Self-hosters can adjust the defaults — see [Environment variables](/self-hosting/environment-variables).

## Sending from a template

You can also send transactional emails using a [template](/concepts/templates) you have created in the dashboard. This allows you to reuse the same design and content for multiple emails, while still personalizing them with contact data.

## Sending later

Add `delivery.at` to send the email at a set time, up to 30 days ahead. Until it goes out you can move or cancel it with its email ID, or cancel it from **Activity** in the dashboard. See [Scheduling](/guides/scheduling).

## Sending at most once per period

Add `delivery.throttle` to send a notification to a recipient at most once per window, such as a usage warning you trigger on every request but want delivered once a day. A throttled send writes nothing and is not billed. See [Throttling](/guides/throttling).

```json
{
  "to": "ana@acme.com",
  "template": "your-template-id",
  "delivery": { "at": "2026-11-01T09:00:00Z", "throttle": "24h" }
}
```

## What's next

<Cards>
  <Card title="Send Email API" href="/api-reference/public-api/sendEmail">
    Full reference for `POST /v1/send`.
  </Card>

  <Card title="Scheduling" href="/guides/scheduling">
    Send later, then move or cancel it before it goes out.
  </Card>

  <Card title="Throttling" href="/guides/throttling">
    Send a notification at most once per period.
  </Card>

  <Card title="Templates" href="/concepts/templates">
    Author reusable email designs.
  </Card>

  <Card title="API keys" href="/guides/api-keys">
    Authenticating requests with `sk_*` and `pk_*` keys.
  </Card>

  <Card title="Webhooks" href="/guides/webhooks">
    Track delivery, opens, clicks, and bounces of your sends.
  </Card>
</Cards>