# Attachments

> For the complete documentation index, see [llms.txt](https://effectkit.dev/llms.txt).

Attach files and inline images to a message as bytes.

Source: https://effectkit.dev/docs/emails/attachments

An attachment is a `Uint8Array` with a file name and a content type. The package copies the bytes and never reads file paths or fetches URLs, so load the file yourself.

**Example** (Attaching a Text File)

```ts twoslash
import { Effect } from "effect";
import { Email } from "@effect-kit/emails";

const program = Effect.gen(function* () {
  const email = yield* Email;
  return yield* email.send({
    from: "billing@example.com",
    to: "ada@example.com",
    subject: "Invoice 1042",
    text: "Your invoice is attached.",
    attachments: [
      {
        filename: "invoice-1042.txt",
        content: new TextEncoder().encode("Total: 42.00"),
        contentType: "text/plain",
      },
    ],
  });
});
```

| Field         | Rules                                                                |
| ------------- | -------------------------------------------------------------------- |
| `filename`    | Not blank, no control characters                                     |
| `content`     | `Uint8Array`                                                         |
| `contentType` | Must look like `type/subtype`                                        |
| `contentId`   | Optional. No whitespace or angle brackets. Unique within the message |

## Inline images [#inline-images]

An attachment with a `contentId` is inline. Reference it from the HTML with a `cid:` URL.

**Example** (Embedding a Logo in the HTML Body)

```ts twoslash
import { Effect } from "effect";
import { Email } from "@effect-kit/emails";

declare const logoPng: Uint8Array;

const program = Effect.gen(function* () {
  const email = yield* Email;
  return yield* email.send({
    from: "hello@example.com",
    to: "ada@example.com",
    subject: "Welcome",
    html: '<img src="cid:logo@example.com" alt="Example" />',
    attachments: [
      {
        filename: "logo.png",
        content: logoPng,
        contentType: "image/png",
        contentId: "logo@example.com",
      },
    ],
  });
});
```

## Provider support [#provider-support]

Attachments and inline images are capabilities, and a message that needs one the provider lacks fails with `UnsupportedFeatureError` before any request.

- No attachments: MailerSend, Brevo and Plunk.
- No inline images: Mailgun, MailerSend, Brevo, Scaleway, Mailchimp Transactional and Plunk.

<Callout type="warn" title="Lettermint content ids">
  Lettermint rejects an inline `contentId` that does not contain `@`, with `InvalidMessageError`.
  Use a qualified id such as `logo@example.com`.
</Callout>