Newsletters from the same API as your receipts.

// 1. Keep a contact up to date, with your own properties.
await coss.email.contacts.upsert({
  email: "ada@example.com",
  first_name: "Ada",
  properties: { plan: "pro" },
});

// 2. A segment that is always current.
const { data: segment } = await coss.email.segments.create({
  name: "Pro customers",
  filter: {
    version: 1,
    match: "all",
    conditions: [{ field: "property", key: "plan", op: "eq", value: "pro" }],
  },
});

// 3. One email to all of it, personalized and paced, next Tuesday at 9:00.
const { data: broadcast } = await coss.email.broadcasts.create({
  name: "October newsletter",
  segment_id: segment?.id,
  topic: "newsletter",
  from: "Acme <news@acme.com>",
  subject: "What's new, {{{contact.first_name|there}}}",
  html: "<p>Hi {{{contact.first_name|there}}}, here is what we shipped.</p>",
  scheduled_at: "2026-11-03T09:00:00Z",
});

Contacts who unsubscribed, opted out of the topic or are on the suppression list are skipped. The API reference lists every field.

coss.com sends transactional and marketing email on separate sending configurations and measures their bounce and complaint rates apart. When marketing email crosses its thresholds, only marketing email is paused, with an account.marketing_paused webhook, and receipts and sign-in links keep going. A complaint about a marketing email suppresses that address for marketing email only.

Consent lives on the contact and deliverability in the suppression list: unsubscribing never adds a suppression, and re-subscribing a contact never removes one, so an address that bounced stays protected. In production environments, a broadcast's content is screened once before it starts.

The dashboard's import reads your old account from Resend, SendGrid or Postmark through its API and brings what you choose into an environment: domains, templates, contacts and their lists, suppressions and webhook endpoints, as each provider allows. Nothing changes in your old account, and the provider's key is deleted when the import ends.

Free includes 3,000 email recipients a month. How many contacts an environment keeps, and how fast broadcasts send, depend on the plan. See pricing for the plans.