Attachments & inline images

Attach files to any send by including base64-encoded content in the attachments array:

{
  "attachments": [
    {
      "filename": "invoice.pdf",
      "content_type": "application/pdf",
      "content": "JVBERi0xLjQK..."
    }
  ]
}

Request bodies are capped at 25 MB; base64 inflates content by ~33%, so that’s roughly an 18 MB attachment budget per email. Invalid base64 is rejected with a validation_error.

Inline images

Give an attachment a content_id and reference it from your HTML with a cid: URL; the attachment is emitted with a matching Content-ID MIME header:

{
  "html": "<p>Cheers!</p><img src=\"cid:logo\">",
  "attachments": [
    { "filename": "logo.png", "content_type": "image/png", "content": "<base64>", "content_id": "logo" }
  ]
}

Retrieving attachments

• GET /emails/{id}/attachments: list an email’s attachments (filename, content type, size).
• GET /emails/{id}/attachments/{attachmentId}: download one.

Inbound mail has the same pair under /emails/received/{id}/attachments; see Inbound email.