MPPtempoquality 0.88

Pay-per-send email delivery via micropayments — no API keys, no accounts, one HTTP request.

Price
$0.005 / call
Protocol
mpp
Verified
no
Endpoint
https://stableemail.dev/api/inbox/send

What it does

StableEmail is a pay-per-send email API that requires no API keys, accounts, or sign-ups. You send a POST request with your email payload, receive a 402 payment challenge, pay in USDC (on Base, Solana, or Tempo), and the email is delivered via AWS SES. The simplest endpoint (`/api/send`) sends from `relay@stableemail.dev` for $0.02 per email. The specific endpoint listed here (`/api/inbox/send`) sends from a purchased forwarding inbox address (e.g., `alice@stableemail.dev`) for $0.005 per email; the payer wallet must be the inbox owner.

Beyond basic sending, StableEmail offers a full inbox and subdomain system. You can buy a forwarding inbox (`username@stableemail.dev`) for $1/month that forwards inbound mail to a real address and/or retains messages for programmatic API access. Inboxes support top-ups with bulk discounts (90 days for $2.50, 365 days for $8) and pro-rata refund on cancellation. Custom subdomains (`yourname.stableemail.dev`) cost $5 one-time and allow sending from any address on that subdomain at $0.005/email, with up to 50 authorized wallet signers. Subdomain inboxes can be created for $0.25 each (max 100 per subdomain, 500 messages each). Reading messages costs $0.001 per call.

All paid endpoints use the x402/MPP protocol — the caller's first request returns HTTP 402 with payment parameters, the caller signs a USDC payment, and resends with the payment header. Free management endpoints (status, update, cancel) use SIWX wallet authentication via the same 402 challenge flow. Attachments are supported (up to 5, ~3.75 MB decoded each), and HTML emails can reference hosted images. Agent integration is available via the `agentcash-skills` MCP server (`npx -y agentcash@latest`).

Capabilities

email-sendemail-receiveemail-forwardinginbox-managementcustom-subdomainattachment-supportmicropayment-authx402-protocolmpp-protocolsiwx-authusdc-paymentprogrammatic-mailboxpro-rata-refund

Use cases

  • —AI agents sending transactional or notification emails without needing API key provisioning
  • —Programmatic email sending from automated workflows paying per message in USDC
  • —Creating disposable or project-specific forwarding inboxes with crypto payments
  • —Receiving and reading inbound emails programmatically via API for agent-driven workflows
  • —Setting up branded email subdomains for projects without traditional email provider configuration

Fit

Best for

  • —AI agents and bots that need to send email without account setup
  • —Developers wanting pay-as-you-go email with no monthly minimums
  • —Crypto-native applications that can pay in USDC on Base, Solana, or Tempo
  • —Lightweight transactional email where traditional provider onboarding is overkill

Not for

  • —High-volume bulk email marketing (no batch/list management features documented)
  • —Users without a crypto wallet or USDC — no traditional payment methods available
  • —Applications requiring custom sender domains outside the stableemail.dev namespace

Quick start

# Send from your inbox address ($0.005 USDC)
# First request returns 402; pay with any x402/MPP client, then:
curl -X POST https://stableemail.dev/api/inbox/send \
  -H 'Content-Type: application/json' \
  -d '{
    "username": "alice",
    "to": ["bob@example.com"],
    "subject": "Hello",
    "text": "Sent from my StableEmail inbox."
  }'

Example

Request

{
  "to": [
    "bob@example.com"
  ],
  "html": "<p>Hi Bob!</p>",
  "text": "Hi Bob!",
  "replyTo": "alice@gmail.com",
  "subject": "Hello from StableEmail",
  "username": "alice"
}

Response

{
  "from": "alice@stableemail.dev",
  "success": true,
  "messageId": "ses-abc123"
}

Endpoint

URLhttps://stableemail.dev/api/inbox/send
Transporthttp
Protocolmpp
CurrencypathUSD

Quality

0.88/ 1.00

Comprehensive OpenAPI 3.1 schema with full request bodies, detailed x-guidance documentation covering all endpoints, clear pricing in USD, and live 402 challenge infrastructure. The specific endpoint probed returned 405 on HEAD/GET because it only accepts POST, which is expected behavior. Minor deductions: no dedicated docs page (404), and response schemas are not formally defined (only described in guidance text).

Warnings

  • —The probe returned 405 on HEAD and GET because /api/inbox/send only accepts POST — this is expected, not an outage.
  • —No formal OpenAPI response schemas are defined; response structures are documented only in the x-guidance text.
  • —The /docs page returns 404; all documentation is embedded in the OpenAPI x-guidance and the landing page.

Citations

Provenance

Indexed frommpp_dev
Enriched2026-04-19 16:06:43Z · anthropic/claude-opus-4.6 · v2
First seen2026-04-18
Last seen2026-04-22

Agent access

JSONhttps://clawmart.sh/api/listings/hn7sNv