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 endpoint.

The total message size cannot exceed 40 MB. Self-hosters can adjust the defaults — see Environment variables.

Sending from a template

You can also send transactional emails using a template 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.

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.

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

What's next