Send an email

Subject, text and HTML

subject is required. Send text, html, or both: with only html, the plain-text version is made from it; with both, text is the plain-text alternative. HTML is made safe on our side — formatting, links, images, tables and inline styles stay; scripts, style sheets, forms, frames, embeds and event handlers are removed; links must be http(s) or mailto, images http(s). In HTML, merge fields such as {{first_name}} and {{company}} are filled in when it goes out (with the contact's values made safe for HTML).

Who it's from

sender_id is the id of an email inbox or a domain sender address from GET /senders. Without it a new email goes out the workspace's usual way, and a reply from the conversation's own inbox. A sender that is disconnected by the time it goes out sends nothing — the message fails with that reason; it never switches to another sender.

Footer and tracking

A one-to-one email gets exactly what the same message sent from the app's inbox gets: your inbox's signature (and its opt-out line where you set one up). Campaign emails — bulk outreach — carry the unsubscribe link and open / click tracking; run those as a campaign.

Attachments

Not available through the API yet — send files as links.

Contacts only

contact_id is a saved contact — there is no field for a typed-in address or number. The contact's own email or phone is used, and only if they have a recorded lawful basis and aren't on your suppression or do-not-contact lists.

Approvals and following it

Every message is an API send: it waits in Approvals when the workspace approves before sending or the key lacks approvals:decide; with approvals:decide, approve: true approves it in the same request. Poll GET /messages/{id} with the answer's id, or subscribe to the message.* webhook events.

Scheduling

Add send_at (RFC 3339 with a zone, in the future, at most 30 days ahead) and nothing goes out before then. The send checks still run at that time, so quiet hours or your sending window can move it to the next allowed moment. It can be approved before then; until it goes out, POST /messages/{id}/cancel stops it.

Many at once

To send to many contacts, use POST /messages/batch: up to 100 items in one request, each with its own result.

Plain text, scheduled

{
  "contact_id": "7d1c3b2a-5e4f-4a1b-9c8d-0e1f2a3b4c5d",
  "channel": "email",
  "subject": "Quick question",
  "text": "Hi Maja, do you have five minutes on Thursday?",
  "send_at": "2026-11-20T08:30:00+01:00"
}

Approve it in the same request (needs approvals:decide)

{
  "contact_id": "7d1c3b2a-5e4f-4a1b-9c8d-0e1f2a3b4c5d",
  "channel": "email",
  "subject": "Your offer",
  "text": "Hi Maja, here it is.",
  "approve": true
}