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You can attach files to any message sent through the Email API. Attachments are added as an attachments array on the message, where each entry describes a single file.
The total size of all attachments must not exceed 50 MB per message. See Limits and overage rates for all sending limits.

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Attachment fields

Each attachment is an object with three required fields:
FieldTypeDescription
fileNamestringName the recipient will see, including the extension (e.g. report.pdf).
contentTypestringValid MIME type for the file, e.g. application/pdf or text/plain.
contentstringThe file contents, Base64-encoded.

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REST API example

Add the attachments array to the message body. The example below attaches a small text file (Hello World! Base64-encoded as SGVsbG8gV29ybGQh): 
{
  "data": {
    "message": {
      "recipients": ["recipient@host.com"],
      "headers": {
        "subject": "Sample email with an attachment",
        "from": "sender@verifieddomain.com"
      },
      "content": {
        "text/plain": "Hello World!"
      },
      "attachments": [
        {
          "fileName": "hello_world.txt",
          "contentType": "text/plain",
          "content": "SGVsbG8gV29ybGQh"
        }
      ]
    }
  }
}
See the full Send a message reference for the complete request body.

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SDK examples

Most Paubox SDKs accept attachments in the same fileName / contentType / content shape. The file content is always Base64-encoded. 
import base64

with open('report.pdf', 'rb') as f:
    encoded = base64.b64encode(f.read()).decode('utf-8')

attachment = {
    'fileName':    'report.pdf',
    'contentType': 'application/pdf',
    'content':     encoded
}

# Pass attachments via the optional_headers dict
optional_headers = {
    'attachments': [attachment]
}
For language-specific details, see each SDK’s email client guide — for example the Python SDK or Node.js SDK.

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Sending from the CLI

The Paubox CLI accepts files directly with the --attachment flag and handles the Base64 encoding for you: 
paubox send \
  --from sender@verifieddomain.com \
  --to recipient@host.com \
  --subject "Sample email with an attachment" \
  --text "Hello World!" \
  --attachment report.pdf
See the CLI commands reference for all available flags.