Use the canonical host
Send paid requests only to https://machineinbox.com and verify the requirement's resource URL before signing.
X402 EMAIL API
Buy an inbox with USDC in the HTTP request.
Every unpaid request returns one HTTP 402 that advertises two rails. A PAYMENT-REQUIRED header carries an x402 v2 requirement for USDC on Base mainnet. A WWW-Authenticate: Payment challenge carries Stripe MPP. Pay with either rail.
- Inbox
- $2.00
- Extension
- $1.00
- Settlement
- USDC on Base
- Protocol
- x402 v2
PAYMENT FLOW
A standard x402 v2 exchange.
- 01
Request
The agent POSTs to the paid route with an
Idempotency-Key. Machine Inbox returns HTTP 402 with a base64PAYMENT-REQUIREDheader describing an exact-scheme USDC payment on Base mainnet (eip155:8453). - 02
Sign
The x402 client signs the payment from its own wallet. Settlement runs through the PayAI facilitator; Machine Inbox never holds your keys.
- 03
Retry and activate
The client retries with one base64
PAYMENT-SIGNATUREheader and the same idempotency key. A successful response contains the inbox address and its bearer token.
BUYER CONTROLS
Keep payment and application retries safe.
Pin the offer
Accept the requirement only when the amount matches the route: $2.00 for the seven-day inbox, $5.00 for the pro inbox, $1.00 for an extension. Reject anything else.
Reuse the key
x402 requests require an idempotency key. Send a unique high-entropy value. Reuse it for the paid retry and for recovery, so a retry cannot buy twice.
RAILS
What each rail covers.
Every paid inbox on both rails includes replies. x402 settlement records on Base mainnet stay public after you erase the mailbox.
| Purchase | x402 (USDC on Base) | Stripe MPP |
|---|---|---|
| Seven-day inbox | $2.00 | $2.00 |
| Thirty-day pro inbox | $5.00 via /api/v1/inboxes/pro | $5.00 |
| Seven-day extension | $1.00 | $1.00 |
| Authenticated replies | Included | Included |