machine inbox

Live · Stripe MPP + x402

Your agent needs
an email address.

No signup, no API key, no OTP sent to a human. One paid request creates a private inbox for your agent. The agent receives mail, reads it through HTTP, and replies in the thread.

Run the quickstart Read llms.txt

One $2.00 payment through Stripe MPP or x402 USDC on Base includes the inbox and authenticated replies. A $5.00 pro inbox lasts thirty days. A $0.05 verification inbox ($0.50 by card) receives one signup code. A $1.00 payment extends any inbox for seven days.

POST /api/v1/inboxes
201

ADDRESS

m_7fa2…c91b@
in.machineinbox.com

Lease
7 days
Storage
25 MiB
Messages
100
Price
$2.00 USD
TOKENmi_live_••••••••

save once · expires on schedule

THE JOB

An inbox that lasts as long as the task.

Use it for verification mail, vendor replies, generated files, support threads, and receipts. Delete it early or let it expire.

  1. 01

    Pay and create

    The first request returns a payment challenge for Stripe MPP and x402. A compatible client pays and retries the request.

  2. 02

    Receive and poll

    Pass the address to any service. List messages with the bearer token returned at creation.

  3. 03

    Reply in-thread

    The inbox includes authenticated replies. The API cannot start a new conversation.

QUICKSTART

A mailbox in three calls.

Stripe's Link CLI and other MPP clients handle the HTTP 402 challenge and paid retry.

OpenAPI JSON ↗ A2A card ↗ Payment metadata ↗ x402 metadata ↗ Buyer examples: MPP + x402 ↗ MCP server ↗
create-inbox.sh 
# Link CLI handles the MPP 402 and paid retry
npx @stripe/link-cli mpp pay \
  https://machineinbox.com/api/v1/inboxes \
  --context "Create one seven-day agent inbox"

# → 201 Created
{
  "inbox": {
    "id": "3bd23...",
    "address": "m_7fa2...@in.machineinbox.com",
    "expiresAt": "2026-08-23T...Z"
  },
  "token": "mi_live_..."
}

API

A small API.
A complete inbox.

The token controls one inbox. Reads and authenticated replies are included. Send an idempotency key so a retry cannot create a duplicate resource.

POST/api/v1/inboxes

Create

POST/api/v1/inboxes/:id/extend

Extend

GET/api/v1/inboxes/:id/messagesincluded

List

GET/api/v1/inboxes/:id/messages/waitincluded

Wait

GET/api/v1/inboxes/:id/verification-codeincluded

Extract code

GET/api/v1/inboxes/:id/messages/:messageIdincluded

Read

POST/api/v1/inboxes/:id/messages/:messageId/replyincluded

Reply

DELETE/api/v1/inboxes/:idincluded

Erase

GUARDRAILS

Useful email, with no spam surface.

The first release accepts inbound mail and sends replies. It cannot start a new conversation.

↩

Reply-only sending

A reply can go only to an authenticated sender address on the source message. No custom recipients, CC, or BCC.

⌛

Short retention

Mail expires with the seven-day lease. Delete the inbox at any time to revoke its token.

#

Hashed credentials

The service stores a token hash. The bearer token appears only in the creation response.

20

Hard send cap

Each inbox can send 20 replies per UTC day. The service blocks bounces, suppressions, and no-reply addresses.

START WITH ONE REQUEST

Give the next task
an address.

Give this API to an agent

Plain-text instructions at /llms.txt