# Mailchimp Transactional (/docs/v/0.6.1/adapters/mailchimp)



The Mailchimp adapter calls the [Mailchimp Transactional API](https://mailchimp.com/developer/transactional/api/messages/send-new-message/) — the API formerly known as Mandrill — over `fetch`, no extra dependency. Unusually, the API key travels in the request body rather than a header, and recipients are a single typed list (`to`/`cc`/`bcc` entries) instead of separate arrays.

<ProviderBadge adapter="mailchimp" />

## Configure [#configure]

Create a Transactional API key in the Mandrill dashboard (Settings → SMTP & API Info) and verify your sending domain.

```ts title="lib/email.ts"
import { createEmailClient } from "@opencoredev/email-sdk";
import { mailchimp } from "@opencoredev/email-sdk/mailchimp";

export const email = createEmailClient({
  adapters: [mailchimp({ apiKey: process.env.MAILCHIMP_API_KEY! })],
});
```

<TypeTable
  type="{
  apiKey: {
    description: &#x22;Mailchimp Transactional (Mandrill) API key, sent in the request body.&#x22;,
    type: &#x22;string&#x22;,
    required: true,
  },
  baseUrl: {
    description: &#x22;Override the API origin, e.g. for a proxy.&#x22;,
    type: &#x22;string&#x22;,
    default: '&#x22;https://mandrillapp.com/api/1.0&#x22;',
  },
  fetch: {
    description: &#x22;Custom fetch implementation for tests or special runtimes.&#x22;,
    type: &#x22;typeof fetch&#x22;,
  },
}"
/>

## Send [#send]

Mailchimp maps `cc`, `bcc`, `headers`, `attachments`, `tags` (values only), and `metadata`.

```ts
const result = await email.send({
  from: "Acme <hello@acme.com>",
  to: [{ email: "user@example.com", name: "Ada" }],
  subject: "Your order has shipped",
  html: "<p>Order ord_123 is on its way.</p>",
  metadata: { orderId: "ord_123" },
  tags: [{ name: "type", value: "shipping" }],
});

console.log(result.id); // Mandrill _id of the first recipient result
```

Mandrill responds with one result per recipient; the normalized `id` and `messageId` come from the first result's `_id`. Each result also carries a per-recipient status (`sent`, `queued`, `rejected`) — check `result.raw` during smoke tests if a send succeeds but mail does not arrive.

<Callout type="warn" title="No replyTo field">
  This adapter does not support `replyTo` — setting it throws an `EmailValidationError` before
  any request is made. Set a `Reply-To` header instead: `headers: { "Reply-To":
    "support@acme.com" }`. See [field support](/docs/v/0.6.1/adapters/field-support) for the full matrix.
</Callout>

## Verify from the CLI [#verify-from-the-cli]

```bash
MAILCHIMP_API_KEY="md-..." npx email-sdk doctor --adapter mailchimp
```

```bash
MAILCHIMP_API_KEY="md-..." npx email-sdk send \
  --adapter mailchimp \
  --from "Acme <hello@acme.com>" \
  --to user@example.com \
  --subject "Mailchimp smoke test" \
  --text "It works" \
  --dry-run
```

Drop `--dry-run` for one real send — that is the only check that proves the key, domain verification, and recipient policy are ready.