{"id":"fd6840a9-1b8d-44d4-b7bb-be94ad22a99e","shortId":"XxpMar","kind":"mpp","title":"Send email from a custom subdomain via micropayment — $0.005/email, no API keys or accounts.","tagline":"Send email from a custom subdomain via micropayment — $0.005/email, no API keys or accounts.","description":"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.\n\nBefore 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.\n\nThe 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.","tags":["email","send","inbox","forwarding","subdomain"],"capabilities":["email-send","custom-subdomain-email","html-email","plain-text-email","attachments","multi-recipient","x402-payment","mpp-payment","usdc-settlement","base-chain","solana-chain","tempo-chain","siwx-auth","wallet-based-identity"],"categories":["email","communication"],"synonyms":["send email API","transactional email","pay-per-send email","micropayment email","subdomain email","custom domain email","x402 email","crypto email API","USDC email","programmatic email"],"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"],"endpointUrl":"https://stableemail.dev/api/subdomain/send","protocol":"mpp","transport":"http","auth":{"type":"mpp","details":{"realm":"stableemail.dev","intent":"charge","method":"tempo","service_methods":{"tempo":{"assets":["0x20c000000000000000000000b9537d11c60e8b50"],"intents":["charge"]}}}},"qualityScore":"0.880","qualityRationale":"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 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'/api/send':208 '/api/subdomain/buy':120 '/api/subdomain/send':33 '/email':10,25,207 '0.005':9,24,49 '0.02':206 '1/month':212 '3.75':182 '402':64 '5':121,129,178 '50':140,162 'USDC email' 'account':15,30,87 'ad':146 'address':41,137,156 'agent':232 'agentcash':238,243 'also':199 'api':12,27,84 'array':158 'attach':82,176 'attachments' 'authent':224 'author':106,141 'avail':235 'aw':193 'base':72 'base-chain' 'base64':180 'base64-encoded':179 'bodi':151 'broader':196 'challeng':65 'client':248 'complet':128 'crypto email API' 'custom':5,20,44 'custom domain email' 'custom-subdomain-email' 'decod':184 'deliv':191 'deriv':91 'dns':126 'domain':203 'e.g':46 'either':166 'email':2,17,38,189 'email-send' 'encod':181 'endpoint':34,111,223 'first':60 'forward':209 'free':221 'header':81 'html':167 'html-email' 'ident':89 'inbox':210,215 'integr':233 'key':13,28,85 'latest':244 'let':35 'limit':185 'localpart@yourname.stableemail.dev':136 'manag':222 'max':177 'mb':183 'mcp':239 'messag':52,218 'micropay':8,23,57 'micropayment email' 'minut':130 'mpp-payment' 'multi-recipient' 'must':99,172 'need':113 'npx':241 'offer':200 'one':123 'one-tim':122 'option':175 'owner':103 'pay-per-send email' 'payer':97 'payment':70,80,94 'per':51,147 'plain-text-email' 'platform':198 'post':119 'programmat':217 'programmatic email' 'protocol':58 'provid':174 'purchas':115 'read':219 'recipi':163 'request':61,150 'requir':152 'resend':77 'return':62 'send':1,16,37,133,204 'send email API' 'server':240 'ses':194 'share':202 'shared-domain':201 'sign':67,228 'sign-in':227 'signer':107,142 'siwx':226 'siwx-auth' 'solana':73 'solana-chain' 'stableemail':31,197 'subdomain':6,21,45,102,117,148,155,214 'subdomain email' 'subject':165 'support':188 'tempo':75 'tempo-chain' 'text':169 'time':124 'transactional email' 'usdc':50,69 'usdc-settlement' 'use':54,109 'verif':127 'via':7,22,118,192,225 'wallet':88,98,143 'wallet-based-identity' 'x':231 'x402 email' 'x402-payment' 'x402/mpp':56 'x402/mpp-compatible':247 'y':242 'you@yourname.stableemail.dev':47","prices":[{"id":"49024393-2817-4f31-b780-37473e6bc54f","listingId":"fd6840a9-1b8d-44d4-b7bb-be94ad22a99e","amountUsd":"0.005","unit":"per_call","nativeCurrency":"pathUSD","nativeAmount":"5000","chain":"tempo","payTo":null,"paymentMethod":"mpp-tempo","isPrimary":true,"details":{"realm":"stableemail.dev","intent":"charge","method":"tempo","dynamic":false,"decimals":6,"unit_type":null,"amount_hint":null,"raw_payment":{"amount":"5000","intent":"charge","method":"tempo","currency":"0x20c000000000000000000000b9537d11c60e8b50","decimals":6,"description":"Send email from custom subdomain"},"asset_contract":"0x20c000000000000000000000b9537d11c60e8b50"},"createdAt":"2026-04-18T19:59:27.452Z"}],"sources":[{"listingId":"fd6840a9-1b8d-44d4-b7bb-be94ad22a99e","source":"mpp_dev","sourceId":"stableemail:POST:/api/subdomain/send","sourceUrl":"https://mpp.dev/api/services","isPrimary":true,"firstSeenAt":"2026-04-18T19:59:27.452Z","lastSeenAt":"2026-04-22T02:45:06.158Z"}],"details":{"listingId":"fd6840a9-1b8d-44d4-b7bb-be94ad22a99e","quickStartSnippet":"curl -X POST https://stableemail.dev/api/subdomain/send \\\n  -H 'Content-Type: application/json' \\\n  -d '{\n    \"from\": \"hello@yourname.stableemail.dev\",\n    \"to\": [\"alice@example.com\"],\n    \"subject\": \"Hello from my subdomain\",\n    \"text\": \"Sent via StableEmail micropayment.\"\n  }'\n# Returns 402 → sign USDC payment → resend with payment header","exampleRequest":{"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"},"exampleResponse":{"from":"hello@yourname.stableemail.dev","success":true,"messageId":"ses-abc123"},"schema":{"path":"/api/subdomain/send","method":"POST","payment":{"amount":"5000","intent":"charge","method":"tempo","currency":"0x20c000000000000000000000b9537d11c60e8b50","decimals":6,"description":"Send email from custom subdomain"},"description":"Send email from custom subdomain"},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"Subdomain send costs $0.005 USDC per email","source_url":"https://stableemail.dev"},{"claim":"Subdomain purchase costs $5 USDC one-time","source_url":"https://stableemail.dev"},{"claim":"Payer wallet must be owner or authorized signer for the subdomain","source_url":"https://stableemail.dev"},{"claim":"Up to 50 authorized wallet signers per subdomain","source_url":"https://stableemail.dev"},{"claim":"Supports Base (eip155:8453), Solana, or Tempo for USDC payment","source_url":"https://stableemail.dev"},{"claim":"Attachments max 5 per email, base64-encoded, ~3.75MB decoded limit each","source_url":"https://stableemail.dev"},{"claim":"Agent integration via agentcash MCP server (npx -y agentcash@latest)","source_url":"https://stableemail.dev"}],"useCases":["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"],"bestFor":["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"],"notFor":["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)"],"kindDetails":{"docs":{"llmsTxt":"https://stableemail.dev/llms.txt","homepage":"https://stableemail.dev"},"tags":["email","send","inbox","forwarding","subdomain"],"realm":"stableemail.dev","status":"active","methods":{"tempo":{"assets":["0x20c000000000000000000000b9537d11c60e8b50"],"intents":["charge"]}},"provider":{"url":"https://stableemail.dev","name":"Merit Systems"},"categories":["social"],"service_id":"stableemail","integration":"first-party","service_name":"StableEmail","service_description":"Pay-per-send email delivery, forwarding inboxes, and custom subdomains — no API keys or accounts."},"updatedAt":"2026-04-22T02:45:06.158Z"}}