> ## Documentation Index
> Fetch the complete documentation index at: https://docs.reallyquickemails.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Attachments

> Attach files (MP3, PDF, .ics) to your sends via URL or base64.

Attach files with the [`POST /send-email`](/en/api-reference/send-email) endpoint. They're specified in the `attachments` field of the body.

<Note>
  This page covers the **API**. You can also attach files from the platform when creating a
  campaign: in the creation panel, under **Attachments**. There you upload files straight from your
  computer (no public URL needed) and the same types and limits below apply.
</Note>

## Attachment structure

Each item in the `attachments` array accepts these fields:

| Field         | Type     | Required    | Description                                                                          |
| ------------- | -------- | ----------- | ------------------------------------------------------------------------------------ |
| `filename`    | `string` | Yes         | File name with extension (e.g. `"invoice.pdf"`).                                     |
| `url`         | `string` | Conditional | Public URL of the file (HTTP or HTTPS). Required if `content` is not used.           |
| `content`     | `string` | Conditional | File content encoded in base64. Required if `url` is not used.                       |
| `contentType` | `string` | No          | MIME type of the file. Auto-detected from the `filename` extension if not specified. |

Each attachment must include `filename` and exactly one of `url` or `content`.

## Allowed types

Only the following MIME types are allowed:

| MIME type         | Extension |
| ----------------- | --------- |
| `application/pdf` | `.pdf`    |
| `text/calendar`   | `.ics`    |
| `audio/mpeg`      | `.mp3`    |

If the MIME type doesn't match these, the send fails in the background (see validation below).

<Warning>
  **Attachments cost you deliverability.** On bulk sends, a binary attachment is a strong spam
  signal and your domain reputation pays for it. For audio or video, a button linking to your own
  page usually works better: lighter, plays in the browser, and tells you who opened it (an
  attachment doesn't).
</Warning>

## Limits

| Limit                         | Value        |
| ----------------------------- | ------------ |
| Maximum number of attachments | 10 per email |
| Maximum size per file         | 10 MB        |
| Maximum total size            | 10 MB        |

## Attachments via URL

With the `url` field, the server downloads the file before sending it. Security measures:

* **HTTP/HTTPS only:** Other URL schemes are rejected.
* **SSRF protection:** URLs pointing to private or reserved IP addresses are blocked.
* **Timeout:** The download has a 30-second limit. If the remote server doesn't respond in time, the send fails.

## Attachments via base64

With the `content` field, the value must be the file encoded in base64 without prefixes (no `data:...;base64,`). Only the raw base64 string.

## Asynchronous validation

The `/send-email` endpoint is asynchronous: the HTTP response confirms the email was queued, but attachments are downloaded and validated **in the background**. If an attachment exceeds the limits, has a disallowed MIME type, or its URL is not accessible, the send fails asynchronously and is recorded in the activity history (`current_status: "failed"`, with the detail in `error_message`).

To confirm the result, query the [Activity API](/en/api-reference/activity) with the `email_id`, or subscribe to [webhooks](/en/api-reference/webhooks).

## Examples

### Attachment via URL

```bash theme={null}
curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Your October invoice",
    "html": "<p>Attached is your October invoice.</p>",
    "attachments": [
      {
        "filename": "invoice-october-2026.pdf",
        "url": "https://storage.example.com/invoices/invoice-october-2026.pdf"
      }
    ]
  }'
```

Response (email queued; attachments are processed in the background):

```json theme={null}
{
  "success": true,
  "queued": true,
  "jobId": "email-1780676307345-6da66195",
  "email_id": "d116a543-9b13-41b4-93cf-647539018275",
  "activityId": "d116a543-9b13-41b4-93cf-647539018275",
  "message": "Email queued for sending"
}
```

### Attachment via base64

```bash theme={null}
curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Meeting invitation",
    "html": "<p>We invite you to a team meeting.</p>",
    "attachments": [
      {
        "filename": "meeting.ics",
        "content": "QkVHSU46VkNBTEVOREFSClZFUlNJT046Mi4wCkJFR0lOOlZFVkVOVApEVFNUQVJUOjIwMjUxMDE2VDE1MDAwMFoKRFRFTkQ6MjAyNTEwMTZUMTYwMDAwWgpTVU1NQVJZOlJldW5pb24gZGUgZXF1aXBvCkVORDpWRVZFTlQKRU5EOlZDQUxFTkRBUg==",
        "contentType": "text/calendar"
      }
    ]
  }'
```

### Multiple attachments

```bash theme={null}
curl -X POST https://api.reallyquickemails.com/send-email \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk_proj_xxxxxxxxxxxx" \
  -d '{
    "recipient": "customer@example.com",
    "sender": "sales@mystore.com",
    "senderName": "My Store",
    "subject": "Project documents",
    "html": "<p>Attached are the contract and the meeting agenda.</p>",
    "attachments": [
      {
        "filename": "contract.pdf",
        "url": "https://storage.example.com/docs/contract.pdf"
      },
      {
        "filename": "agenda.ics",
        "content": "QkVHSU46VkNBTEVOREFSClZFUlNJT046Mi4wCkVORDpWQ0FMRU5EQVI=",
        "contentType": "text/calendar"
      }
    ]
  }'
```

The response uses the same `queued` structure as the first example. The `attachments` field is not validated in the HTTP response; check the final status with the [Activity API](/en/api-reference/activity).