Campaigns

A campaign is a newsletter: one email to a whole audience, or to a segment or topic within it. Everything the composer in the app does is available here, so you can draft from a script or from an AI editor and still hand a human an editable campaign to look at before it goes out.

Sending is the one part of this API that is genuinely irreversible, so it sits behind its own scope.

The Campaign object


{
  "id": "cmp_4v0dz1k9x2m7",
  "object": "campaign",
  "name": "August release",
  "subject": "What shipped in August",
  "preview_text": "Sending domains, faster imports, and a new API.",
  "status": "draft",
  "sandbox": false,
  "audience_id": "aud_7k2m9x4v0dz1",
  "segment_id": null,
  "topic_id": null,
  "sender_id": "snd_2v0dz1k9x4m",
  "sending_domain_id": "dom_9x4v0dz1k2m",
  "from_name": "Acme",
  "from_email": "hello@yourdomain.com",
  "reply_to": null,
  "footer_text": null,
  "risk_level": null,
  "risk_summary": null,
  "paused_reason": null,
  "scheduled_at": null,
  "sent_at": null,
  "created_at": "2026-08-20T09:00:00.000Z",
  "updated_at": "2026-08-20T09:00:00.000Z",
  "url": "https://go.day3.app/campaigns/cmp_4v0dz1k9x2m7"
}

url is where a human goes to look at it. Every write hands it back, so you never have to assemble the link yourself.

Campaign bodies

Give the body as exactly one of these:

Field	Use it when
`markdown`	Almost always. day3 Markdown, described below.
`sections`	You are round-tripping the composer’s own structure.
`html`	You have finished HTML. It is sanitized and stored without structure.

markdown is preferred because each construct becomes a real editable block in the visual composer, so what you write by API stays editable by hand. html is the opposite: it goes in as one opaque block.

day3 Markdown

Ordinary Markdown, plus a few block constructs:


# Heading            (through ######)
Plain paragraphs, **bold**, *italic*, `code`, [links](https://example.com)
- bullet / 1. numbered lists
---                                        a horizontal rule
![Alt](https://cdn.example.com/a.png)      an image, alone on its own line
[![Alt](img-url)](link-url)                an image that links somewhere
[Label](https://x.com){.button}            a call-to-action button
    options: {.button bg=#2563eb color=#ffffff full align=left}
> A quote                                  a callout box
> -- Attribution                           optional attribution line
:::spacer 48:::                            blank vertical space, in pixels

:::columns                                 two or three side-by-side columns
### Left
Text.
+++
### Right
Text.
:::

:::card image-left                         an image paired with text
![Alt](https://cdn.example.com/p.png)      (also image-right / image-top)

Text beside the image.
:::

:::social Follow us:                       a row of profile links
- twitter: https://x.com/acme              (twitter, linkedin, facebook,
- website: https://acme.com                 instagram, youtube, github,
:::                                         website, email)

:::section {bg=#f5f5f5 align=center}       tint or align a block
Anything above.
:::

:::html                                    raw HTML, sanitized on the way in
<table><tr><td>Anything the blocks
above cannot express.</td></tr></table>
:::

===                                        force a split between two text blocks

The attribution line inside a quote must start with -- (or an en or em dash). A plain line is read as more of the quote.

:::html is the escape hatch, and it costs you something: it goes in as one opaque block, so a human cannot edit it in the composer the way they can edit everything else. Reach for it last.

Images must be absolute https URLs that are already hosted publicly. The API cannot upload files.

Personalization: {{first_name}}, {{last_name}} and {{email}} are merged per recipient, along with any custom field key. Give blank-safe copy a fallback: {{first_name|there}}.

The footer’s postal address and unsubscribe link are appended automatically and cannot be removed. That is a compliance requirement, not a setting.

List campaigns

GET/v1/campaigns

Newest first, cursor-paginated. Filter with ?status=.

Create a draft

POST/v1/campaigns

Every field is optional. A draft is allowed to be incomplete, exactly as in the app, so you can create one and fill it in later.

Field	Notes
`subject`	The subject line.
`markdown` / `sections` / `html`	The body. Exactly one.
`name`	Internal name, never shown to recipients.
`preview_text`	Inbox preview text.
`audience_id`	Defaults to your only audience, when there is exactly one.
`segment_id`	Send to a segment instead of the whole audience.
`topic_id`	Send only to contacts subscribed to a topic.
`sender_id`	Defaults to the account’s default sender.
`from_name`, `reply_to`, `footer_text`	Override the sender defaults.


curl -X POST https://go.day3.app/api/v1/campaigns \
  -H "Authorization: Bearer $DAY3_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
        "subject": "What shipped in August",
        "preview_text": "Sending domains, faster imports, and a new API.",
        "markdown": "# August\n\nHi {{first_name|there}}, here is what changed.\n\n[Read the changelog](https://day3.app/changelog){.button}"
      }'

Retrieve a campaign

GET/v1/campaigns/{campaign_id}

Returns the campaign plus its body in all three representations: markdown, sections and html.

Read before editing. A PATCH that sends markdown replaces the body, so writing without reading first discards any change a human made in the composer.

Update a campaign

PATCH/v1/campaigns/{campaign_id}

Same fields as create. Only what you send changes.

Returns 409 once the campaign has left draft or scheduled. A campaign that is sending or sent is immutable.

Delete a campaign

DELETE/v1/campaigns/{campaign_id}

Drafts and scheduled campaigns only. A sent campaign is a record and stays.

Preview a campaign

GET/v1/campaigns/{campaign_id}/preview

The rendered email, with the theme, merge tags and the compliance footer applied. Add ?format=html to get the HTML document itself rather than a JSON wrapper.

This is what you show a human, or read back to check your Markdown produced the blocks you expected.

Send a test

POST/v1/campaigns/{campaign_id}/test


{ "to": "you@example.com" }

to is an address or an array of up to 5. A test goes only to the addresses you name and never to the audience.

Test sends deliberately need no scope. They are the whole point of letting a script or an agent iterate on an email, and they cannot reach your list.

Send to the audience

POST/v1/campaigns/{campaign_id}/sendscope: campaigns:send

This sends to the whole audience, immediately. There is no confirmation step and no undo. It starts the automated risk review, and delivery follows if that passes.

Requires a key with the campaigns:send scope, which is off by default and cannot be added to an existing key. If the key lacks it you get 403 insufficient_scope: mint a key with sending enabled rather than working around it.

Schedule a send

POST/v1/campaigns/{campaign_id}/schedulescope: campaigns:send


{ "send_at": "2026-09-01T09:00:00Z" }

At least a minute in the future. Same scope and the same consequences as sending, just later.

Cancel a schedule

DELETE/v1/campaigns/{campaign_id}/schedule

Returns the campaign to draft. Needs no scope, because un-sending is always safe.

Sandbox mode

On a free plan a campaign send is real but reaches only members of your own organization, and the campaign carries "sandbox": true. The allowance is 100 emails a month, shared with API and test sends. See Authentication.

Sending a series instead

A campaign is one email to a whole audience at one moment. A welcome series, a trial drip or an onboarding sequence is an automation: built on the canvas in the app, and enrolled into one contact at a time from your own backend.