Attachments

Loomal supports file attachments on both inbound and outbound emails. Attachment metadata is returned on every message and thread response. Binary content is fetched via a dedicated download endpoint.

Limits

Limit	Value
Per attachment	10 MB
Per email (total)	25 MB
Per email (count)	10 attachments

Sending attachments

POST /v0/messages/send and POST /v0/messages/:id/reply accept an attachments array. Each attachment carries the file content as base64.

{
  "to": ["user@example.com"],
  "subject": "Quarterly report",
  "text": "See attached.",
  "attachments": [
    {
      "filename": "Q1-report.pdf",
      "contentType": "application/pdf",
      "data": "JVBERi0xLjQKJeLjz9MK..."
    }
  ]
}

Field	Type	Description
`filename`	`string`	Display name (max 255 chars)
`contentType`	`string`	MIME type (e.g. `application/pdf`, `image/png`)
`data`	`string`	Base64-encoded file content

Attachment metadata in responses

GET /v0/messages, GET /v0/messages/:id, GET /v0/threads/:id, and the send/reply responses all include an attachments array per message:

{
  "messageId": "<abc@mailgent.dev>",
  "subject": "Quarterly report",
  "...": "...",
  "attachments": [
    {
      "attachmentId": "cm9k2x4f80001abc",
      "filename": "Q1-report.pdf",
      "contentType": "application/pdf",
      "size": 2148532,
      "inline": false,
      "contentId": null,
      "createdAt": "2026-04-07T12:00:00.000Z"
    }
  ]
}

Downloading attachment bytes

Scope: mail:read

Streams the raw file bytes with the original Content-Type and a Content-Disposition: attachment header.

Request

mail.get_attachment(message_id, attachment_id)

The MCP tool returns the file as base64 inside the JSON-RPC response so the agent can process it immediately without a separate HTTP call. Available through @loomal/mcp — see MCP setup.

curl -O \
  -H "Authorization: Bearer loid-your-api-key" \
  https://api.loomal.ai/v0/messages/%3Cabc%40mailgent.dev%3E/attachments/cm9k2x4f80001abc

The messageId must be URL-encoded (it contains <>@).

The Node and Python SDKs do not expose attachment downloads — call REST directly or use the MCP tool.

Endpoint

GET /v0/messages/{messageId}/attachments/{attachmentId}

Errors

Status	Code	Description
`404`	`not_found`	Attachment doesn't exist or doesn't belong to the message/inbox