# Message (/docs/reference/message)



## `EmailMessage` [#emailmessage]

```ts
type EmailMessage = {
  from: EmailAddress;
  to: EmailAddress | EmailAddress[];
  subject: string;
  html?: string;
  text?: string;
  cc?: EmailAddress | EmailAddress[];
  bcc?: EmailAddress | EmailAddress[];
  replyTo?: EmailAddress | EmailAddress[];
  headers?: Record<string, string> | EmailHeader[];
  attachments?: EmailAttachment[];
  tags?: EmailTag[];
  metadata?: Record<string, string | number | boolean | null>;
  idempotencyKey?: string;
};
```

Every message must include:

* `from`
* at least one `to`
* `subject`
* `html` or `text`

## Addresses [#addresses]

An address can be a string or an object with a display name.

```ts
const from = "Acme <hello@acme.com>";

const to = {
  email: "user@example.com",
  name: "Ada Lovelace",
};
```

## Attachments [#attachments]

```ts
type EmailAttachment = {
  filename: string;
  content?: string | Uint8Array | ArrayBuffer | Blob;
  contentEncoding?: "raw" | "base64";
  path?: string;
  contentType?: string;
  contentId?: string;
  disposition?: "attachment" | "inline";
};
```

Use `content` for in-memory attachments. String content is treated as raw content and encoded to Base64 for API providers that require it. Use `contentEncoding: "base64"` when the string is already Base64.

Use `path` when you want Email SDK to read a local file before sending. See <a href="/docs/adapters/field-support">field support</a> for adapter-specific attachment support.

## Headers and tags [#headers-and-tags]

Headers can be an object or a list:

```ts
headers: {
  "X-Order-ID": "ord_123";
}
```

Tags are provider-specific. Resend accepts `tags`. Postmark maps the first tag to its `Tag` field.