{"id":"83dae75f-5d6b-4805-9dbd-d6bd6f1324f7","shortId":"hn7sNv","kind":"mpp","title":"Pay-per-send email delivery via micropayments — no API keys, no accounts, one HTTP request.","tagline":"Pay-per-send email delivery via micropayments — no API keys, no accounts, one HTTP request.","description":"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.\n\nBeyond 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.\n\nAll 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`).","tags":["email","send","inbox","forwarding","subdomain"],"capabilities":["email-send","email-receive","email-forwarding","inbox-management","custom-subdomain","attachment-support","micropayment-auth","x402-protocol","mpp-protocol","siwx-auth","usdc-payment","programmatic-mailbox","pro-rata-refund"],"categories":["email","communication"],"synonyms":["send email API","pay per email","micropayment email","x402 email","transactional email","email forwarding","programmatic inbox","USDC email","no-signup email API","crypto email service"],"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."],"endpointUrl":"https://stableemail.dev/api/inbox/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":"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).","verified":false,"liveness":"unknown","lastLivenessCheck":null,"agentReviews":{"count":0,"score_avg":null,"cost_usd_avg":null,"success_rate":null,"latency_p50_ms":null,"narrative_summary":null,"summary_updated_at":null},"enrichmentModel":"anthropic/claude-opus-4.6","enrichmentVersion":2,"enrichedAt":"2026-04-19T16:06:43.436Z","embedding":[0.023239136,-0.025924683,0.025436401,0.029891968,0.015174866,-0.032196045,-0.03390503,0.022491455,0.0552063,-0.05831909,0.038146973,-0.014533997,-0.020553589,-0.02357483,-0.0032978058,0.013000488,-0.014266968,-0.013793945,-0.04159546,0.024307251,0.06976318,0.015075684,-0.0023784637,0.0463562,-0.008743286,-0.011489868,-0.027328491,-0.007850647,0.028182983,-0.06732178,0.06854248,-0.045928955,-0.017364502,0.005870819,-0.018066406,0.058166504,-0.037872314,0.07287598,0.02319336,0.019500732,-0.013931274,-0.038269043,0.016296387,-0.004550934,-0.05206299,0.03643799,0.005466461,-0.018447876,0.029159546,0.02255249,-0.006175995,0.022979736,0.00315094,0.024642944,0.029464722,0.017211914,0.024475098,0.024520874,-0.020492554,0.017501831,0.02128601,-0.028335571,-0.054901123,-0.020309448,0.008766174,0.032470703,-0.011627197,0.039276123,0.008636475,0.08856201,0.031402588,0.009819031,0.037475586,-0.026824951,-0.00021386147,-0.033233643,0.03237915,0.018920898,0.013015747,-0.03466797,-0.004837036,-0.013763428,-0.028579712,0.015037537,-0.021087646,-0.015914917,-0.023071289,0.009277344,0.0025520325,0.0025539398,-0.07287598,-0.0045166016,-0.000100791454,-0.00579834,0.02178955,-0.036010742,-0.036743164,0.011360168,-0.015037537,0.0127334595,0.033081055,-0.05255127,-0.036956787,-0.055908203,0.028213501,0.024337769,0.051483154,0.015182495,0.016860962,0.015144348,-0.0715332,0.020889282,-0.01272583,-0.00025892258,0.032226562,0.008598328,-0.0132369995,0.0026168823,-0.032409668,-0.013504028,-0.03100586,0.053771973,0.02607727,0.010803223,0.0121536255,-0.042053223,-0.045135498,-0.010299683,0.0046577454,0.029800415,0.047973633,0.009552002,0.06604004,-0.0048217773,-0.032714844,0.044708252,-0.008483887,-0.02571106,-0.014228821,0.010345459,0.04776001,-0.025146484,0.012542725,0.008842468,-0.03274536,-0.008338928,-0.0501709,-0.01612854,-0.015777588,0.0022659302,0.0287323,-0.017303467,-0.02166748,0.009048462,-0.03213501,0.025222778,-0.009399414,0.057769775,-0.006755829,-0.019744873,-0.0028591156,0.00945282,-0.0029640198,-0.037200928,0.00415802,-0.0060272217,0.037078857,-0.07525635,-0.04083252,-0.016174316,-0.0043945312,-0.027664185,-0.017333984,0.008010864,0.02130127,-0.051330566,0.008850098,-0.016937256,-0.0072402954,-0.012390137,0.026733398,0.041534424,-0.0085372925,0.0126571655,-0.005466461,-0.02027893,-0.007549286,0.049346924,0.008323669,0.023666382,0.0008659363,-0.021255493,-0.0026054382,0.03982544,-0.020202637,-0.006626129,0.03955078,0.026885986,-0.025970459,0.01928711,0.00028300285,-0.02456665,0.029647827,0.07330322,-0.025405884,-0.004573822,0.011665344,0.017044067,-0.01701355,0.028259277,0.046966553,0.007537842,-0.004283905,0.014755249,-0.07849121,-0.03488159,-0.040649414,-0.03564453,0.037719727,0.058380127,-0.0071983337,-0.009994507,0.005367279,0.031173706,-0.024673462,0.02104187,0.05999756,-0.0016489029,-0.016555786,-0.023117065,0.009170532,0.023513794,-0.013336182,0.012329102,-0.016296387,0.0044021606,-0.02255249,-0.027435303,0.0043144226,0.0124435425,-0.025054932,-0.014343262,-0.016082764,0.020935059,-0.0008831024,0.019927979,-0.023040771,-0.03692627,0.0446167,0.02029419,0.06567383,-0.0042152405,-0.015258789,-0.053253174,0.0027427673,-0.044799805,0.030227661,-0.0022907257,0.026947021,-0.021850586,0.016799927,-0.03781128,-0.022338867,0.0040779114,0.02130127,0.01399231,0.015487671,-0.0024051666,-0.029312134,0.045166016,0.013626099,0.057525635,0.040130615,0.014083862,0.008125305,0.0057029724,0.012901306,-0.03604126,-0.026809692,0.052856445,-0.03074646,-0.027877808,-0.006832123,-0.047454834,0.038024902,0.023483276,0.0040397644,-0.015060425,0.04840088,-0.026000977,-0.014343262,0.05291748,0.019836426,-0.009735107,0.029037476,-0.015602112,0.043029785,-0.024612427,0.0362854,0.008041382,0.030776978,0.034332275,0.0015926361,-0.066223145,-0.009666443,0.024475098,0.02355957,0.045837402,0.0146102905,-0.019180298,-0.023880005,0.030517578,-0.01638794,0.020843506,0.0063285828,0.021133423,0.004501343,0.0019292831,-0.054473877,-0.064208984,-0.024429321,0.04296875,0.0181427,-0.019592285,0.02078247,-0.0040740967,0.018218994,-0.016616821,-0.026000977,-0.029083252,0.011940002,-0.043121338,0.0038337708,-0.035705566,0.004802704,0.006580353,0.030700684,-0.008506775,0.0025405884,0.06719971,-0.021697998,-0.04248047,-0.01574707,-0.029800415,-0.039398193,-0.025283813,-0.02519226,0.003824234,0.022018433,0.022857666,-0.051483154,0.04876709,0.040496826,0.028808594,0.039978027,0.005958557,0.022613525,-0.097595215,-0.03302002,-0.01914978,-0.015625,0.04537964,-0.0042762756,0.014770508,0.05731201,0.030822754,-0.041778564,-0.046722412,0.045806885,-0.041625977,0.0814209,0.06854248,0.02142334,0.030975342,0.013618469,-0.013038635,0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'/api/send':85 '/email':197 '0.001':223 '0.005':109,196 '0.02':90 '0.25':211 '1/month':139 '100':214 '2.50':166 '3.75':278 '365':167 '402':63,240,269 '5':182,277 '50':201 '500':217 '8':170 '90':163 'USDC email' 'access':154 'account':13,29,47 'address':105,147,191 'agent':289 'agentcash':296,302 'agentcash-skil':295 'alice@stableemail.dev':107 'allow':187 'and/or':148 'api':10,26,41,45,153 'attach':272 'attachment-support' 'authent':265 'author':202 'avail':292 'aw':80 'base':70 'basic':121 'beyond':120 'bulk':161 'buy':133 'call':225 'caller':234,245 'cancel':177,261 'challeng':65,270 'cost':181,222 'creat':209 'crypto email service' 'custom':178 'custom-subdomain' 'day':164,168 'decod':280 'deliv':78 'deliveri':6,22 'discount':162 'e.g':106 'email':5,21,40,59,76,92,111,284 'email forwarding' 'email-forwarding' 'email-receive' 'email-send' 'endpoint':84,95,228,258 'first':236 'flow':271 'forward':103,135,141 'free':256 'full':126 'header':255 'host':287 'html':283 'http':15,31,239 'imag':288 'inbound':142 'inbox':104,118,127,136,155,206 'inbox-management' 'integr':290 'key':11,27,46 'latest':303 'list':96 'mail':143 'manag':257 'max':213 'mb':279 'mcp':298 'messag':150,218,221 'micropay':8,24 'micropayment email' 'micropayment-auth' 'mpp-protocol' 'must':115 'no-signup email API' 'npx':300 'offer':124 'one':14,30,184 'one-tim':183 'owner':119 'paid':227 'paramet':243 'pay':2,18,37,66 'pay per email' 'pay-per-send':1,17,36 'payer':113 'payload':60 'payment':64,242,249,254 'per':3,19,38,91,110,215,224 'post':55 'pro':173 'pro-rata':172 'pro-rata-refund' 'programmat':152 'programmatic inbox' 'programmatic-mailbox' 'protocol':232 'purchas':102 'rata':174 'read':220 'real':146 'receiv':61 'refer':286 'refund':175 'relay@stableemail.dev':88 'request':16,32,56,237 'requir':43 'resend':251 'retain':149 'return':238 'send':4,20,39,53,86,99,122,188 'send email API' 'server':299 'ses':81 'sign':50,246 'sign-up':49 'signer':204 'simplest':83 'siwx':263 'siwx-auth' 'skill':297 'solana':71 'specif':94 'stableemail':33,123 'status':259 'subdomain':129,179,194,205,216 'support':156,274 'system':130 'tempo':73 'time':185 'top':158 'top-up':157 'transactional email' 'up':51,159 'updat':260 'usdc':68,248 'usdc-payment' 'use':229,262 'username@stableemail.dev':137 'via':7,23,79,266,293 'wallet':114,203,264 'x402 email' 'x402-protocol' 'x402/mpp':231 'y':301 'yourname.stableemail.dev':180","prices":[{"id":"8ba3be0a-50ba-4bb0-a931-ab8629721e78","listingId":"83dae75f-5d6b-4805-9dbd-d6bd6f1324f7","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 inbox address"},"asset_contract":"0x20c000000000000000000000b9537d11c60e8b50"},"createdAt":"2026-04-18T19:59:29.397Z"}],"sources":[{"listingId":"83dae75f-5d6b-4805-9dbd-d6bd6f1324f7","source":"mpp_dev","sourceId":"stableemail:POST:/api/inbox/send","sourceUrl":"https://mpp.dev/api/services","isPrimary":true,"firstSeenAt":"2026-04-18T19:59:29.397Z","lastSeenAt":"2026-04-22T02:45:06.237Z"}],"details":{"listingId":"83dae75f-5d6b-4805-9dbd-d6bd6f1324f7","quickStartSnippet":"# Send from your inbox address ($0.005 USDC)\n# First request returns 402; pay with any x402/MPP client, then:\ncurl -X POST https://stableemail.dev/api/inbox/send \\\n  -H 'Content-Type: application/json' \\\n  -d '{\n    \"username\": \"alice\",\n    \"to\": [\"bob@example.com\"],\n    \"subject\": \"Hello\",\n    \"text\": \"Sent from my StableEmail inbox.\"\n  }'","exampleRequest":{"to":["bob@example.com"],"html":"<p>Hi Bob!</p>","text":"Hi Bob!","replyTo":"alice@gmail.com","subject":"Hello from StableEmail","username":"alice"},"exampleResponse":{"from":"alice@stableemail.dev","success":true,"messageId":"ses-abc123"},"schema":{"path":"/api/inbox/send","method":"POST","payment":{"amount":"5000","intent":"charge","method":"tempo","currency":"0x20c000000000000000000000b9537d11c60e8b50","decimals":6,"description":"Send email from inbox address"},"description":"Send email from inbox address"},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"Send from inbox address costs $0.005 USDC per email","source_url":"https://stableemail.dev"},{"claim":"Forwarding inbox costs $1/month (30 days), with quarterly ($2.50) and yearly ($8) bulk discounts","source_url":"https://stableemail.dev"},{"claim":"Custom subdomains cost $5 one-time purchase","source_url":"https://stableemail.dev"},{"claim":"Basic send from relay@stableemail.dev costs $0.02 per email","source_url":"https://stableemail.dev"},{"claim":"Payments accepted in USDC on Base, Solana, or Tempo via x402/MPP protocol","source_url":"https://stableemail.dev"},{"claim":"Email delivered via AWS SES","source_url":"https://stableemail.dev"},{"claim":"Subdomain inboxes cost $0.25 to create, max 100 per subdomain, 500 messages each","source_url":"https://stableemail.dev/.well-known/x402"},{"claim":"Agent integration available via agentcash-skills MCP server","source_url":"https://stableemail.dev"}],"useCases":["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"],"bestFor":["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"],"notFor":["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"],"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":"2026-04-22T02:45:06.237Z"}}