Segments

A segment is a saved, reusable filter over the contacts on one of your sending domains. Instead of sending a campaign to a domain’s entire contact pool, you can target a segment — a subset matched by a filter. A segment belongs to exactly one domain: names are unique within a domain but freely reusable across domains, and every domain also carries an auto-created General segment that matches all of its contacts.

Segments are for your own internal organization — they are never visible to your contacts. Use them to group contacts however makes sense for your sending (by signup source, plan, engagement, email domain, and so on).

Filters

A segment filter has two parts, combined with AND:

Create a segment

import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.segments.create({
  "domain": "yourdomain.com",
  "name": "Gmail subscribers",
  "filter": { "status": "subscribed", "email_contains": "@gmail.com" }
});
console.log({ data, error });

Preview who matches

List the contacts a segment currently resolves to — useful to sanity-check a filter before sending.

const { data } = await mb.segments.contacts('seg_9a2f...');
console.log(data.data.length, 'contacts match');

Send a campaign to a segment

Pass segment_id when creating a campaign. The campaign then fans out only to the segment’s matching contacts (still excluding anyone unsubscribed, for compliance).

await mb.campaigns.create({
  domain: 'yourdomain.com',
  segment_id: 'seg_9a2f...',
  from: 'Acme <news@yourdomain.com>',
  subject: 'A note for our Gmail folks',
  html: '<p>Hi {{FIRST_NAME}}</p>',
});