Email broadcasts
Send newsletters and announcements to a segment of your contacts from the dashboard, the API, or an AI agent. Schedule sends, A/B test subject lines and content, and track results per campaign.
Send to any segment
Target a static list or a rule-based segment. Personalise every message with contact names and properties, and let unsubscribed and suppressed addresses drop out automatically.
Built-in A/B testing
Test two to five subject-line or content variants on a sample of 5–50% of the segment. After your chosen window, the variant with the best open rate goes to everyone else.
Scheduling and cancellation
Send now or schedule for a future time. Cancel a queued broadcast before it goes out, or stop one mid-send — recipients not yet reached will not get it.
Create and send a broadcast
const broadcast = await poststack.broadcasts.create({
name: 'March Newsletter',
segment_id: 'seg_newsletter',
from: 'news@yourdomain.com',
subject: "What's new in March",
html: '<h1>Hi {{first_name}}</h1><p>Here is what shipped…</p>',
scheduled_at: '2026-03-28T09:00:00Z',
});
await poststack.broadcasts.send(broadcast.id);Use cases
Monthly newsletters
Write the newsletter once, schedule it for a time that suits your audience, and watch opens, clicks, bounces, and unsubscribes roll up in the dashboard as they arrive.
Product launches and release notes
Segment by plan or signup date so the launch announcement only reaches customers who will care, and A/B test the subject line on a sample before the rest of the list receives the winner.
Re-engagement campaigns
Build a segment of contacts who have not opened an email in 60 days, send them a focused re-engagement broadcast, then use the results to decide who to keep mailing — protecting your sender reputation.
Event invitations and reminders
Schedule the invitation and each reminder as separate broadcasts to the same segment, or use a workflow with wait steps to automate the sequence per contact.
How it works
A broadcast is one message sent to every contact in a segment. You create it with a from address on a verified domain, a subject, and an HTML and/or plain-text body, then send it immediately or set `scheduled_at` for later. Merge tags such as `{{first_name}}` are resolved per recipient from contact data, and every broadcast is sent with RFC 8058 one-click unsubscribe headers so Gmail and Yahoo show their native unsubscribe button. Contacts who are unsubscribed or on your suppression list are skipped automatically. Sending runs in batches through the same pipeline as the transactional API — same DKIM signing, same bounce and complaint handling, same webhook events. A/B testing is built in: define two to five variants of the subject and content, choose a test sample between 5% and 50% of the segment and a decision window between 30 minutes and 24 hours, and PostStack sends the variants to the sample, waits, and sends the variant with the highest open rate to everyone else. You can also pick the winner early by hand. Broadcast status moves through draft, queued, sending, sent, or cancelled; cancelling a queued or in-progress broadcast stops any messages that have not been sent yet but cannot recall ones already delivered. Per-broadcast performance — sent, delivered, opened, clicked, bounced, complained, unsubscribed — is available in the dashboard and through the MCP server, including a list of recipients who received it but did not click, for a targeted follow-up.
Full parameters, limits, and examples are in the Email broadcasts documentation.
Frequently asked questions
How do broadcasts differ from transactional sends?
Transactional sends are triggered by your application, usually to one recipient, and go out immediately. Broadcasts target a segment of contacts, can be scheduled, always carry one-click unsubscribe headers, support A/B testing, and report results at the campaign level.
Do you support A/B testing?
Yes — two to five variants per broadcast. Choose a test sample (5–50% of the segment) and a decision window (30 minutes to 24 hours). The variant with the highest open rate is then sent to the rest of the segment automatically, or you can pick a winner early.
Can I cancel a scheduled broadcast?
Yes. Cancelling a queued broadcast stops it entirely. Cancelling one that is already sending stops the remaining batches, but messages already delivered cannot be recalled.
What happens to unsubscribes?
An unsubscribe marks the contact as unsubscribed and adds the address to your suppression list immediately, so it is excluded from future sends. Every broadcast carries RFC 8058 one-click unsubscribe headers, and you can add a visible `{{unsubscribe_url}}` link to the body.
Are broadcasts included on the free plan?
Yes. Broadcasts, contacts, and segments are available on every plan, including Free. Broadcast emails count toward your monthly email allowance like any other send.