{"id":"75cf241e-d96d-47e7-a4aa-6f4efd133ab3","shortId":"EhTXeS","kind":"mpp","title":"Pay-per-send email delivery via micropayments — $0.02/email, no API keys, no accounts.","tagline":"Pay-per-send email delivery via micropayments — $0.02/email, no API keys, no accounts.","description":"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.\n\nBeyond 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.\n\nAll 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.","tags":["email","send","inbox","forwarding","subdomain"],"capabilities":["email-send","email-receive","email-forwarding","custom-subdomain","inbox-management","attachment-support","calendar-invite","micropayment-auth","x402-protocol","mpp-protocol","siwx-auth","programmatic-mailbox","pro-rata-refund","multi-chain-payment"],"categories":["email","communication"],"synonyms":["send email API","pay per email","micropayment email","x402 email","transactional email","email relay","forwarding inbox","programmatic mailbox","USDC email","no-signup email API"],"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."],"endpointUrl":"https://stableemail.dev/api/send","protocol":"mpp","transport":"http","auth":{"type":"mpp","details":{"realm":"stableemail.dev","intent":"charge","method":"tempo","service_methods":{"tempo":{"assets":["0x20c000000000000000000000b9537d11c60e8b50"],"intents":["charge"]}}}},"qualityScore":"0.920","qualityRationale":"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 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'/call':181 '/email':10,25,122 '0.001':180 '0.005':121 '0.02':9,24,65 '0.25':138 '1/month':156 '100':142 '2.50':163 '3.1':243 '3.75':186 '365':164 '402':60 '5':113,185 '50':125 '8':167 '90':160 'USDC email' 'account':15,30,45 'address':136 'agent':220 'agentcash':227,233 'agentcash-skil':226 'also':147 'api':12,27,39,43,178 'attach':182 'attachment-support' 'authent':217 'author':126 'automat':239 'aw':78 'base':69,216 'beyond':97 'bodi':54 'bulk':158 'calendar':190 'calendar-invite' 'cancel':171,211 'catch':130 'catch-al':129 'challeng':62 'check':208 'custom':105 'custom-subdomain' 'day':161,165 'deliv':76 'deliveri':6,21 'discount':159 'document':248 'domain':153 'email':5,20,38,74 'email relay' 'email-forwarding' 'email-receive' 'email-send' 'endpoint':196,199,206 'entir':83 'flow':84 'forward':132,148 'forwarding inbox' 'free':204 'full':241 'guidanc':247 'handl':236 'http':88 'inbox':137,149 'inbox-management' 'integr':221 'invit':191 'json':53 'key':13,28,44 'latest':234 'llms.txt':246 'manag':205 'mb':187 'mcp':229 'messag':175 'micropay':8,23,95 'micropayment email' 'micropayment-auth' 'mpp-protocol' 'multi-chain-payment' 'negoti':203,238 'no-signup email API' 'npx':231 'offer':104 'one':99,111 'one-off':98 'one-tim':110 'openapi':242 'origin':253 'paid':198 'path':222 'pay':2,17,35,64 'pay per email' 'pay-per-send':1,16,34 'payment':61,114,202,237 'per':3,18,36,117,135,143 'per-address':134 'per-subdomain':116 'post':51 'pro':169 'pro-rata':168 'pro-rata-refund' 'programmat':174 'programmatic mailbox' 'programmatic-mailbox' 'protocol':96 'publish':250 'rata':170 'read':176 'receiv':58 'recommend':219 'refund':172 'relay':101 'relay@stableemail.dev':81 'requir':41 'round':90 'round-trip':89 'send':4,19,37,102,119,195 'send email API' 'server':230 'ses':79 'set':209 'share':152 'sign':48 'sign-up':47 'signer':128 'singl':87 'siwx':213 'siwx-auth' 'skill':228 'solana':70 'spec':244 'stableemail':31,103 'status':207 'subdomain':106,118,144 'support':193 'tempo':72 'time':112 'transactional email' 'trip':91 'up':49 'updat':210 'usdc':67 'use':92,200,212 'username@stableemail.dev':154 'via':7,22,77,177,224 'wallet':127,215 'wallet-bas':214 'x402 email' 'x402-protocol' 'x402/mpp':94,201 'y':232 'yourname.stableemail.dev':107","prices":[{"id":"e8a5b70c-e681-48ee-beb0-f158acff3d6f","listingId":"75cf241e-d96d-47e7-a4aa-6f4efd133ab3","amountUsd":"0.02","unit":"per_call","nativeCurrency":"pathUSD","nativeAmount":"20000","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":"20000","intent":"charge","method":"tempo","currency":"0x20c000000000000000000000b9537d11c60e8b50","decimals":6,"description":"Send email from relay address"},"asset_contract":"0x20c000000000000000000000b9537d11c60e8b50"},"createdAt":"2026-04-18T19:59:27.008Z"}],"sources":[{"listingId":"75cf241e-d96d-47e7-a4aa-6f4efd133ab3","source":"mpp_dev","sourceId":"stableemail:POST:/api/send","sourceUrl":"https://mpp.dev/api/services","isPrimary":true,"firstSeenAt":"2026-04-18T19:59:27.008Z","lastSeenAt":"2026-04-22T02:45:06.147Z"}],"details":{"listingId":"75cf241e-d96d-47e7-a4aa-6f4efd133ab3","quickStartSnippet":"# Send an email for $0.02 USDC (handles 402 payment automatically)\nnpx agentcash fetch POST https://stableemail.dev/api/send \\\n  --body '{\"to\":[\"alice@example.com\"],\"subject\":\"Hello\",\"text\":\"Sent via StableEmail\"}'","exampleRequest":{"to":["alice@example.com"],"text":"Sent and paid in one HTTP request.","replyTo":"you@example.com","subject":"Hello from StableEmail"},"exampleResponse":{"from":"relay@stableemail.dev","success":true,"messageId":"ses-abc123"},"schema":{"path":"/api/send","method":"POST","payment":{"amount":"20000","intent":"charge","method":"tempo","currency":"0x20c000000000000000000000b9537d11c60e8b50","decimals":6,"description":"Send email from relay address"},"description":"Send email from relay address"},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"Send email from relay@stableemail.dev costs $0.02 USDC","source_url":"https://stableemail.dev"},{"claim":"Custom subdomain purchase costs $5 USDC one-time","source_url":"https://stableemail.dev"},{"claim":"Forwarding inbox costs $1/month with bulk discounts ($2.50/90d, $8/365d)","source_url":"https://stableemail.dev"},{"claim":"Supports payment on Base, Solana, or Tempo networks in USDC","source_url":"https://stableemail.dev"},{"claim":"Email delivered via AWS SES","source_url":"https://stableemail.dev"},{"claim":"Agent integration via agentcash-skills MCP server","source_url":"https://stableemail.dev"},{"claim":"Up to 5 attachments per email, ~3.75MB decoded limit each","source_url":"https://stableemail.dev/.well-known/x402"},{"claim":"Subdomain inboxes cost $0.25 each, max 100 per subdomain, 500 messages each","source_url":"https://stableemail.dev/.well-known/x402"},{"claim":"Pro-rata USDC refund on inbox cancellation","source_url":"https://stableemail.dev"}],"useCases":["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"],"bestFor":["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"],"notFor":["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)"],"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":"2026-04-22T02:45:06.147Z"}}