Client domains (sub-tenancy)

If you're an agency or a platform, client domains let each of your customers send from their own address with their own reputation — isolated from one another and from you. Provision a client, hand back the DNS records, verify them, then send scoped to that client.

Send as a client

Scope any request to a client with mail.withSubTenant(id) (SDK) or the X-Rootmail-Subtenant header (HTTP). The client's contacts, suppression list, audit trail, and reputation all stay their own.

const client = await mail.subTenants.create({
  name: "Sunset Villas",
  sendingDomain: "sunsetvillas.com",
});
// hand client.dns_records to your customer, then:
await mail.subTenants.verify(client.id);

await mail.withSubTenant(client.id).messages.create({
  to: "guest@example.com",
  subject: "Your booking is confirmed",
  html: "<h1>See you soon!</h1>",
});

The scope applies to READS as well as sends. With the header set, listing messages, or asking for analytics or deliverability, returns that client's numbers alone — so you can build a per-client view without filtering client-side. Leave it off and you get the whole workspace, every client included.

const acme = mail.withSubTenant(client.id);

await acme.messages.list();      // only Acme's mail
await acme.analytics.get();      // only Acme's funnel
await acme.deliverability.get(); // only Acme's reputation

await mail.messages.list();      // everything, all clients

In the dashboard this is the client switcher in the top bar: pick a client and every section narrows to them until you leave.

• One client's bounce or complaint never touches another's deliverability.
• Everything rolls up to you for billing and oversight.
• Client domains are sold per-domain — buy them with a plan or on their own.