npm install @resend/chat-sdk-adapter chat @chat-adapter/state-memory
# or: yarn add / pnpm add / bun add

import { createResendAdapter } from '@resend/chat-sdk-adapter';
import { MemoryStateAdapter } from '@chat-adapter/state-memory';
import { Chat } from 'chat';

const resend = createResendAdapter({
  fromAddress: 'bot@example.com',
  fromName: 'My Bot', // optional
  // apiKey: "re_...",       // or set RESEND_API_KEY env var
  // webhookSecret: "whsec_..." // or set RESEND_WEBHOOK_SECRET env var
});

const chat = new Chat({
  userName: 'email-bot',
  adapters: { resend },
  state: new MemoryStateAdapter(),
});

// New email (new thread)
chat.onNewMention(async (thread, message) => {
  await thread.subscribe();
  await thread.post(`Got your email: ${message.text}`);
});

// Follow-up email in a subscribed thread
chat.onSubscribedMessage(async (thread, message) => {
  await thread.post(`Reply: ${message.text}`);
});

// Inside your HTTP server handler for POST /webhook
const result = await chat.webhooks.resend(request);

await thread.post({
  card: {
    type: 'card',
    title: 'Order Confirmed',
    children: [
      { type: 'text', content: 'Your order #1234 has been shipped.' },
      { type: 'divider' },
      {
        type: 'link-button',
        label: 'Track Order',
        url: 'https://example.com/track/1234',
      },
    ],
  },
  fallbackText: 'Order #1234 confirmed',
});

const threadId = await chat.adapters.resend.openDM('user@example.com');
const thread = await chat.thread('resend', threadId);
await thread.post('Hello from the bot!');

chat.onNewMention(async (thread, message) => {
  const attachments = message.raw?.attachments ?? [];
  for (const file of attachments) {
    console.log(file.filename, file.contentType, file.url);
  }
});

# Resend Chat SDK Adapter

**Purpose:** Instructions for building bidirectional email bots using the `@resend/chat-sdk-adapter` package with the Vercel Chat SDK.

***

## Setup

### Prerequisites

- Resend API key stored in `RESEND_API_KEY` env var
- Verified domain at https://resend.com/domains
- Webhook configured for `email.received` events (see [https://resend.com/docs/webhooks/introduction](/guides/learn-webhooks-introduction))
- Inbound email receiving enabled (see [https://resend.com/docs/dashboard/receiving/introduction](/guides/learn-dashboard-receiving-introduction))

### Install

```bash theme={"theme":{"light":"github-light","dark":"vesper"}}
npm install @resend/chat-sdk-adapter chat @chat-adapter/state-memory
# or: yarn add / pnpm add / bun add
```

### Initialize

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
import { createResendAdapter } from '@resend/chat-sdk-adapter';
import { MemoryStateAdapter } from '@chat-adapter/state-memory';
import { Chat } from 'chat';

const resend = createResendAdapter({
  fromAddress: 'bot@example.com',
  fromName: 'My Bot', // optional
  // apiKey: "re_...",       // or set RESEND_API_KEY env var
  // webhookSecret: "whsec_..." // or set RESEND_WEBHOOK_SECRET env var
});

const chat = new Chat({
  userName: 'email-bot',
  adapters: { resend },
  state: new MemoryStateAdapter(),
});
```

### Handle Inbound Emails

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
// New email (new thread)
chat.onNewMention(async (thread, message) => {
  await thread.subscribe();
  await thread.post(`Got your email: ${message.text}`);
});

// Follow-up email in a subscribed thread
chat.onSubscribedMessage(async (thread, message) => {
  await thread.post(`Reply: ${message.text}`);
});
```

### Forward Webhooks

Point Resend webhooks to your server's `/webhook` endpoint. The adapter handles verification and parsing.

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
// Inside your HTTP server handler for POST /webhook
const result = await chat.webhooks.resend(request);
```

`request` must be a Web `Request` object. If you're using Node.js `http`, convert `IncomingMessage` to a `Request` first.

***

## Configuration

| Parameter       | Type     | Required | Description                                                           |
| --------------- | -------- | -------- | --------------------------------------------------------------------- |
| `fromAddress`   | `string` | Yes      | Sender email address                                                  |
| `fromName`      | `string` | No       | Display name for the From header                                      |
| `apiKey`        | `string` | No       | Resend API key. Falls back to `RESEND_API_KEY` env var                |
| `webhookSecret` | `string` | No       | Webhook signing secret. Falls back to `RESEND_WEBHOOK_SECRET` env var |

***

## Threading

Threads are resolved automatically using `Message-ID`, `In-Reply-To`, and `References` headers. Reply chains are grouped into Chat SDK threads with no extra configuration.

***

## Card Emails

Send rich HTML emails using Card elements:

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
await thread.post({
  card: {
    type: 'card',
    title: 'Order Confirmed',
    children: [
      { type: 'text', content: 'Your order #1234 has been shipped.' },
      { type: 'divider' },
      {
        type: 'link-button',
        label: 'Track Order',
        url: 'https://example.com/track/1234',
      },
    ],
  },
  fallbackText: 'Order #1234 confirmed',
});
```

Cards render to HTML via `@react-email/components`. Always include `fallbackText` for plain-text clients.

***

## Proactive Outreach

Start a new email thread without waiting for inbound:

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
const threadId = await chat.adapters.resend.openDM('user@example.com');
const thread = await chat.thread('resend', threadId);
await thread.post('Hello from the bot!');
```

***

## Attachments

Inbound email attachments are available on `message.raw.attachments`:

```typescript theme={"theme":{"light":"github-light","dark":"vesper"}}
chat.onNewMention(async (thread, message) => {
  const attachments = message.raw?.attachments ?? [];
  for (const file of attachments) {
    console.log(file.filename, file.contentType, file.url);
  }
});
```

***

## Unsupported Operations

Email is immutable. These operations throw `NotImplementedError`:

- `editMessage` / `deleteMessage`
- `addReaction` / `removeReaction`
- `startTyping`

***

## AI Model Instructions

1. **Always** use `createResendAdapter` from `@resend/chat-sdk-adapter`
2. **Always** store API keys in env vars, never hardcode
3. **Always** call `thread.subscribe()` in `onNewMention` if you want to receive follow-ups
4. **Always** include `fallbackText` when sending card emails
5. **Never** attempt `editMessage`, `deleteMessage`, `addReaction`, `removeReaction`, or `startTyping` — email does not support these
6. The webhook handler expects a Web `Request` object — convert Node.js `IncomingMessage` if needed
7. The adapter name in Chat config must be `"resend"` for thread routing to work

For the full Resend docs: [https://resend.com/docs/llms-full.txt](/llms-full.txt)