# Attachments

> Attach files to an email as base64 content or a hosted URL, with per-file and total size limits.

Add files to an email with the `attachments` array. Each attachment is either inlined as **base64** `content` or referenced by a hosted **`path`** URL that MailBlastr fetches when the email is sent.

## Attachment fields

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `filename` | string | Yes | The name the file is presented with in the recipient's mail client (e.g. `invoice.pdf`). |
| `content` | string | No | The file contents, base64-encoded. Provide either `content` **or** `path`. |
| `path` | string | No | A hosted URL MailBlastr fetches at send time. Provide either `path` **or** `content`. The fetch is SSRF-guarded. |
| `content_type` | string | No | Optional MIME type for the attachment (e.g. `application/pdf`). Inferred from the filename when omitted. |
| `content_id` | string | No | Embeds the attachment as an inline image; reference it in your HTML via `<img src="cid:...">`. Only meaningful when the attachment is an image. |

> **Warning:** Each attachment must provide exactly one of `content` or `path`. An attachment with neither is rejected.

## Size limits

| Limit | Value |
| --- | --- |
| Per attachment | up to 25 MB |
| Total per email | up to 40 MB |

These limits cover the decoded bytes. Note that base64 encoding inflates the payload by roughly 33%, so a 25 MB file is about 34 MB of `content` in the request body. For large files, prefer `path` so MailBlastr streams the bytes server-side.

> **Warning:** Attachments are **not supported on the batch endpoint** ([POST /emails/batch](https://www.mailblastr.com/docs/emails/batch)). To send an email with an attachment, use a single [POST /emails](https://www.mailblastr.com/docs/api/emails-send) request.

## Send with an attachment (hosted URL)

The simplest form points `path` at a hosted file — MailBlastr fetches it at send time, so you never base64-encode anything yourself.

**Node.js**

```js
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "path": "https://yourdomain.com/invoices/invoice.pdf"
    }
  ]
});
console.log({ data, error });
```

**Ruby**

```ruby
require "mailblastr"

Mailblastr.api_key = "mb_xxxxxxxxx"

Mailblastr::Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "path": "https://yourdomain.com/invoices/invoice.pdf"
    }
  ]
})
```

**PHP**

```php
$mailblastr = Mailblastr::client('mb_xxxxxxxxx');

$mailblastr->emails->send([
  'from' => "Acme <hello@yourdomain.com>",
  'to' => [
    "delivered@example.com"
  ],
  'subject' => "Your invoice",
  'html' => "<p>Invoice attached.</p>",
  'attachments' => [
    [
      'filename' => "invoice.pdf",
      'path' => "https://yourdomain.com/invoices/invoice.pdf"
    ]
  ]
]);
```

**Python**

```python
import mailblastr

mailblastr.api_key = "mb_xxxxxxxxx"

mailblastr.Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "path": "https://yourdomain.com/invoices/invoice.pdf"
    }
  ]
})
```

**Go**

```go
import "github.com/shekhu10/mailblastr-sdks/mailblastr-go"

client := mailblastr.NewClient("mb_xxxxxxxxx")

params := &mailblastr.SendEmailRequest{
    From:    "Acme <hello@yourdomain.com>",
    To:      []string{"delivered@example.com"},
    Subject: "hello world",
    Html:    "<p>it works!</p>",
}
sent, err := client.Emails.Send(params)
```

**Rust**

```rust
use mailblastr::{Mailblastr, CreateEmailBaseOptions};

let mb = Mailblastr::new("mb_xxxxxxxxx");

let email = CreateEmailBaseOptions::new(
    "Acme <hello@yourdomain.com>",
    ["delivered@example.com"],
    "hello world",
).with_html("<p>it works!</p>");
let _sent = mb.emails.send(email).await?;
```

**Java**

```java
import com.mailblastr.*;

Mailblastr mailblastr = new Mailblastr("mb_xxxxxxxxx");

SendEmailRequest request = SendEmailRequest.builder()
    .from("Acme <hello@yourdomain.com>")
    .to("delivered@example.com")
    .subject("hello world")
    .html("<p>it works!</p>")
    .build();
mailblastr.emails().send(request);
```

**.NET**

```csharp
using Mailblastr;

IMailblastr mailblastr = MailblastrClient.Create("mb_xxxxxxxxx");

var resp = await mailblastr.EmailSendAsync(new EmailMessage
{
    From = "Acme <hello@yourdomain.com>",
    To = "delivered@example.com",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
});
```

**cURL**

```bash
curl -X POST 'https://api.mailblastr.com/emails' \
  -H 'Authorization: Bearer mb_xxxxxxxxx' \
  -H 'Content-Type: application/json' \
  -d '{
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "path": "https://yourdomain.com/invoices/invoice.pdf"
    }
  ]
}'
```

> **Note:** A `path` URL is fetched through an SSRF-guarded client and must return the file with a 2xx status. If the fetch fails or the file exceeds the size limit, the send is rejected with a `validation_error`.

## Send with base64 content

Or inline the bytes directly as base64 `content` — useful for files you generate in memory and never host.

**Node.js**

```js
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr('mb_xxxxxxxxx');

const { data, error } = await mb.emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "content": "JVBERi0xLjQKJ...base64...",
      "content_type": "application/pdf"
    }
  ]
});
console.log({ data, error });
```

**Ruby**

```ruby
require "mailblastr"

Mailblastr.api_key = "mb_xxxxxxxxx"

Mailblastr::Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "content": "JVBERi0xLjQKJ...base64...",
      "content_type": "application/pdf"
    }
  ]
})
```

**PHP**

```php
$mailblastr = Mailblastr::client('mb_xxxxxxxxx');

$mailblastr->emails->send([
  'from' => "Acme <hello@yourdomain.com>",
  'to' => [
    "delivered@example.com"
  ],
  'subject' => "Your invoice",
  'html' => "<p>Invoice attached.</p>",
  'attachments' => [
    [
      'filename' => "invoice.pdf",
      'content' => "JVBERi0xLjQKJ...base64...",
      'content_type' => "application/pdf"
    ]
  ]
]);
```

**Python**

```python
import mailblastr

mailblastr.api_key = "mb_xxxxxxxxx"

mailblastr.Emails.send({
  "from": "Acme <hello@yourdomain.com>",
  "to": [
    "delivered@example.com"
  ],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "content": "JVBERi0xLjQKJ...base64...",
      "content_type": "application/pdf"
    }
  ]
})
```

**Go**

```go
import "github.com/shekhu10/mailblastr-sdks/mailblastr-go"

client := mailblastr.NewClient("mb_xxxxxxxxx")

params := &mailblastr.SendEmailRequest{
    From:    "Acme <hello@yourdomain.com>",
    To:      []string{"delivered@example.com"},
    Subject: "hello world",
    Html:    "<p>it works!</p>",
}
sent, err := client.Emails.Send(params)
```

**Rust**

```rust
use mailblastr::{Mailblastr, CreateEmailBaseOptions};

let mb = Mailblastr::new("mb_xxxxxxxxx");

let email = CreateEmailBaseOptions::new(
    "Acme <hello@yourdomain.com>",
    ["delivered@example.com"],
    "hello world",
).with_html("<p>it works!</p>");
let _sent = mb.emails.send(email).await?;
```

**Java**

```java
import com.mailblastr.*;

Mailblastr mailblastr = new Mailblastr("mb_xxxxxxxxx");

SendEmailRequest request = SendEmailRequest.builder()
    .from("Acme <hello@yourdomain.com>")
    .to("delivered@example.com")
    .subject("hello world")
    .html("<p>it works!</p>")
    .build();
mailblastr.emails().send(request);
```

**.NET**

```csharp
using Mailblastr;

IMailblastr mailblastr = MailblastrClient.Create("mb_xxxxxxxxx");

var resp = await mailblastr.EmailSendAsync(new EmailMessage
{
    From = "Acme <hello@yourdomain.com>",
    To = "delivered@example.com",
    Subject = "hello world",
    HtmlBody = "<p>it works!</p>",
});
```

**cURL**

```bash
curl -X POST 'https://api.mailblastr.com/emails' \
  -H 'Authorization: Bearer mb_xxxxxxxxx' \
  -H 'Content-Type: application/json' \
  -d '{
  "from": "Acme <hello@yourdomain.com>",
  "to": ["delivered@example.com"],
  "subject": "Your invoice",
  "html": "<p>Invoice attached.</p>",
  "attachments": [
    {
      "filename": "invoice.pdf",
      "content": "JVBERi0xLjQKJ...base64...",
      "content_type": "application/pdf"
    }
  ]
}'
```