MPPtempoquality 0.88

Send email from a custom subdomain via micropayment — $0.005/email, no API keys or accounts.

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

What it does

StableEmail's `/api/subdomain/send` endpoint lets you send email from any address on a custom subdomain (e.g., `you@yourname.stableemail.dev`) for $0.005 USDC per message. It uses the x402/MPP micropayment protocol: the first request returns a 402 challenge, you sign a USDC payment on Base, Solana, or Tempo, then resend with the payment header attached. No API keys, no accounts — wallet identity is derived from the payment itself. The payer wallet must be the subdomain owner or an authorized signer.

Before using this endpoint you need to purchase a subdomain via `POST /api/subdomain/buy` ($5 one-time). Once DNS verification completes (~5 minutes), you can send from any `localpart@yourname.stableemail.dev` address. Up to 50 authorized signer wallets can be added per subdomain. The request body requires `from` (your subdomain address), `to` (array of up to 50 recipients), and `subject`. Either `html` or `text` (or both) must be provided. Optional attachments (max 5, base64-encoded, ~3.75 MB decoded limit each) are supported. Emails are delivered via AWS SES.

The broader StableEmail platform also offers shared-domain sending at $0.02/email (`/api/send`), forwarding inboxes at $1/month (`/api/inbox/buy`), subdomain inboxes with programmatic message reading, and free management endpoints authenticated via SIWX (Sign-In With X). Agent integration is available through the agentcash MCP server (`npx -y agentcash@latest`) or any x402/MPP-compatible client.

Capabilities

email-sendcustom-subdomain-emailhtml-emailplain-text-emailattachmentsmulti-recipientx402-paymentmpp-paymentusdc-settlementbase-chainsolana-chaintempo-chainsiwx-authwallet-based-identity

Use cases

  • —AI agents sending branded emails from a custom subdomain without managing SMTP credentials
  • —Automated notifications or alerts from a dedicated subdomain address
  • —Wallet-authenticated email sending where the payer's crypto wallet serves as identity
  • —Sending transactional emails with attachments (invoices, receipts, calendar invites) at $0.005 each
  • —Multi-tenant apps where each tenant gets a subdomain with authorized signer wallets

Fit

Best for

  • —AI agents and bots that need to send email programmatically without API key management
  • —Developers who want pay-per-use email with crypto micropayments instead of monthly subscriptions
  • —Projects needing branded subdomain email without configuring DNS, DKIM, or SMTP servers

Not for

  • —High-volume bulk/marketing email campaigns (50 recipients per call limit, per-send cost)
  • —Users who need traditional email accounts with IMAP/POP access
  • —Organizations requiring email sending from their own top-level domain (only *.stableemail.dev subdomains)

Quick start

curl -X POST https://stableemail.dev/api/subdomain/send \
  -H 'Content-Type: application/json' \
  -d '{
    "from": "hello@yourname.stableemail.dev",
    "to": ["alice@example.com"],
    "subject": "Hello from my subdomain",
    "text": "Sent via StableEmail micropayment."
  }'
# Returns 402 → sign USDC payment → resend with payment header

Example

Request

{
  "to": [
    "alice@example.com"
  ],
  "from": "hello@yourname.stableemail.dev",
  "html": "<p>This email was sent via StableEmail.</p>",
  "text": "This email was sent via StableEmail.",
  "replyTo": "you@example.com",
  "subject": "Hello from my subdomain"
}

Response

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

Endpoint

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

Quality

0.88/ 1.00

Full OpenAPI 3.1 schema with detailed request bodies, clear pricing ($0.005 USDC), comprehensive guidance document, and live endpoint (POST-only, so HEAD/GET returning 405 is expected). Docs page returns 404 but the llms.txt guidance is thorough. Minor gap: no captured 402 challenge on this specific endpoint since the probe only tried HEAD/GET.

Warnings

  • —Probe returned 405 because HEAD/GET were tried on a POST-only endpoint; the endpoint is expected to be live for POST requests
  • —The /docs page returns 404; all documentation comes from the OpenAPI spec and llms.txt guidance
  • —Subdomains are under *.stableemail.dev only — you cannot use your own top-level domain

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/XxpMar