Attachments

Attach files to a send, reply, or forward, then list or download attachment parts from a received message. The key needs the mailbox:send permission string to send attachments and mailbox:read to list or download them. These names are stable wire values.

Sending attachments

Add an attachments array to a send, reply, or forward body. Each entry contains standard base64 file bytes and optional filename and content_type. Extrovert builds the multipart MIME message.

Attachments survive the Review Loop: a queued message keeps its files (and its reply_to and custom headers) on the review row, and the approved send delivers them. A redraft via submit_revision may replace them: supply attachments to swap the set, omit the field to leave it untouched, or pass [] to clear it. The human reviews the message the recipient gets.

curl

curl -sS -X POST "$EXTROVERT_API_BASE_URL/v1/inboxes/agent7%40extrovertmail.com/send" \
  -H "Authorization: Bearer $EXTROVERT_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "to": ["ops@acme.test"],
    "subject": "report",
    "text": "Attached.",
    "intent": { "summary": "Send ops the weekly deploy report they asked for" },
    "attachments": [
      { "filename": "report.pdf", "content_type": "application/pdf", "content_base64": "JVBERi0…" }
    ]
  }'

TypeScript SDK

send-with-attachment.ts

import { readFileSync } from "node:fs";

await inbox.send({
  to: "ops@acme.test",
  subject: "report",
  text: "Attached.",
  intent: { summary: "Send ops the weekly deploy report they asked for" },
  attachments: [
    {
      filename: "report.pdf",
      content_type: "application/pdf",
      content_base64: readFileSync("report.pdf").toString("base64"),
    },
  ],
});

MCP

send_email (tool call)

{
  "name": "send_email",
  "arguments": {
    "inbox": "agent7@extrovertmail.com",
    "to": ["ops@acme.test"],
    "subject": "report",
    "text": "Attached.",
    "intent": { "summary": "Send ops the weekly deploy report they asked for" },
    "attachments": [
      { "filename": "report.pdf", "content_type": "application/pdf", "content_base64": "JVBERi0…" }
    ]
  }
}

Body size

The request body is capped at about 25 MB. Base64 adds about 33% overhead, leaving roughly 18 MB for attachment bytes after the rest of the request.

Listing and downloading

A received message exposes attachment metadata first. Download the bytes using the part’s opaque id.

You want	Endpoint	SDK	MCP
List attachment metadata	GET …/messages/{id}/attachments	inbox.attachments(msgId)	list_attachments
Download one part’s bytes	GET …/messages/{id}/attachments/{attId}	inbox.attachment(msgId, attId)	get_attachment

# 1. list: { items: [{ id, filename, content_type, size }], total }
curl -sS "$EXTROVERT_API_BASE_URL/v1/inboxes/agent7%40extrovertmail.com/messages/msg_8Tz/attachments" \
  -H "Authorization: Bearer $EXTROVERT_API_KEY"

# 2. download: raw bytes with Content-Type + Content-Disposition set
curl -sS "$EXTROVERT_API_BASE_URL/v1/inboxes/agent7%40extrovertmail.com/messages/msg_8Tz/attachments/att_1" \
  -H "Authorization: Bearer $EXTROVERT_API_KEY" -o invoice.pdf

The REST download response returns raw bytes and sets Content-Type and Content-Disposition from the part. The MCP get_attachment tool returns base64 content in its structured result. Neither path requires parsing the raw MIME message.

Next

• Messages, threads and search
• API: Messages and threads
• Webhooks and HMAC