MPPtempoquality 0.92

Pay-per-send email delivery via micropayments — $0.02/email, no API keys, no accounts.

Price
$0.02 / call
Protocol
mpp
Verified
no
Endpoint
https://stableemail.dev/api/send

What it does

StableEmail is a pay-per-send email API that requires no API keys, accounts, or sign-ups. You POST a JSON body to `/api/send` and receive a 402 payment challenge; after paying $0.02 in USDC (on Base, Solana, or Tempo) the email is delivered via AWS SES from `relay@stableemail.dev`. The entire flow is a single HTTP round-trip using the x402/MPP micropayment protocol.

Beyond one-off relay sends, StableEmail offers custom subdomains (`yourname.stableemail.dev` for a one-time $5 payment) with per-subdomain sending at $0.005/email, up to 50 authorized wallet signers, catch-all forwarding, and per-address inboxes ($0.25 each, up to 100 per subdomain). There are also forwarding inboxes on the shared domain (`username@stableemail.dev`) at $1/month with bulk discounts (90 days for $2.50, 365 days for $8), pro-rata cancellation refunds, and programmatic message reading via API at $0.001/call. Attachments (up to 5, ~3.75 MB each) and calendar invites are supported on send endpoints.

All paid endpoints use x402/MPP payment negotiation; free management endpoints (status checks, settings updates, cancellation) use SIWX wallet-based authentication. The recommended agent integration path is via the `agentcash-skills` MCP server (`npx -y agentcash@latest`), which handles payment negotiation automatically. A full OpenAPI 3.1 spec and `llms.txt` guidance document are published at the origin.

Capabilities

email-sendemail-receiveemail-forwardingcustom-subdomaininbox-managementattachment-supportcalendar-invitemicropayment-authx402-protocolmpp-protocolsiwx-authprogrammatic-mailboxpro-rata-refundmulti-chain-payment

Use cases

  • —AI agents sending transactional or notification emails without managing API keys
  • —Developers prototyping email features without signing up for an email provider
  • —Creating disposable or forwarding inboxes for privacy or project isolation
  • —Automated workflows that need to send occasional emails and pay per use
  • —Programmatic reading of inbound emails for agent-driven customer support or monitoring

Fit

Best for

  • —AI agents and bots that need email send/receive without credentials
  • —Low-volume transactional email where per-send pricing beats monthly plans
  • —Privacy-conscious users wanting forwarding inboxes with no account signup
  • —Crypto-native applications that can pay with USDC on Base, Solana, or Tempo

Not for

  • —High-volume bulk email or marketing campaigns (per-send cost adds up quickly)
  • —Users without crypto wallets or USDC (no traditional payment rails available)
  • —Email requiring custom DKIM/SPF on your own domain (sends from stableemail.dev subdomains only)

Quick start

# Send an email for $0.02 USDC (handles 402 payment automatically)
npx agentcash fetch POST https://stableemail.dev/api/send \
  --body '{"to":["alice@example.com"],"subject":"Hello","text":"Sent via StableEmail"}'

Example

Request

{
  "to": [
    "alice@example.com"
  ],
  "text": "Sent and paid in one HTTP request.",
  "replyTo": "you@example.com",
  "subject": "Hello from StableEmail"
}

Response

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

Endpoint

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

Quality

0.92/ 1.00

Full OpenAPI 3.1 spec with detailed request schemas, comprehensive guidance document covering all endpoints, clear pricing in USD, and a live 402 challenge (endpoint is POST-only, so HEAD/GET returning 405 is expected). The only gap is that response schemas are not formally defined beyond summaries, and there is no dedicated docs page (returns 404).

Warnings

  • —The probe's HEAD/GET attempts returned 405 because /api/send is POST-only; the endpoint is live and healthy.
  • —No formal response schemas in the OpenAPI spec — response structures are documented only in the guidance text.
  • —The /docs page returns 404; all documentation is embedded in the OpenAPI x-guidance field and /llms.txt.

Citations

Provenance

Indexed frommpp_dev
Enriched2026-04-19 16:05:05Z · anthropic/claude-opus-4.6 · v2
First seen2026-04-18
Last seen2026-04-22

Agent access

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