Let Agents In

Agent readiness · Transactional email APIs

postmarkapp.com

11 of 14 measurable points under formula 9.2, measured on 2026-08-12. 15 checks exist; each is one HTTP request with a published rule, so every sentence below can be rerun and argued with. 1 of them could not be measured from where we ask, and those are left out of the denominator rather than counted as failures.

A · Discovery

  • PASS
    Answers an agent user-agentAnswered 200 to LetAgentsIn/1.0 (+https://letagentsin.com/methodology) across three tries (200, 429, 200)
  • PASS
    llms.txt publishedllms.txt present at https://postmarkapp.com/llms.txt, and the 12 links we sampled across the file all answer
  • PASS
    Docs readable without JavaScript9,027 characters of text without JS
  • PASS
    On-demand agents not blockedExplicitly allowed: ChatGPT-User, Claude-User
  • N/A
    Paths robots.txt points at answerrobots.txt names no concrete path, only patterns or nothing, so there is no claim to check
  • PASS
    No punishing crawl delayNo Crawl-delay applies to the agents we check

B · Agent entry

  • UNMEASURED
    Agent entry pointUnmeasurable: 2 of the 9 known agent entry paths answered with a refusal rather than a file or a 404, so what you publish there is not something we measuredLet ordinary HTTP reach these paths and this becomes measurable.
  • FAIL
    OAuth dynamic client registrationNo OAuth metadata on any of the 9 hosts probed, including the usual auth and api subdomains
  • FAIL
    MCP surfaceNo MCP surface: nothing answered at mcp.postmarkapp.com, mcp.postmarkapp.com/mcp, mcp.postmarkapp.com/v1/mcp, api.postmarkapp.com/mcp, /mcp or /api/mcp, and no file mentions MCP

C · Registration

  • FAIL
    No CAPTCHA in the signup HTMLrecaptcha appears in the signup page's server HTML
  • PASS
    Signup reachable without a browserForm renders in server HTML at https://account.postmarkapp.com/sign_up

D · Provisioning

  • PASS
    Programmatic key provisioning2 of 7 provisioning phrases across the 3 documents we read: "management api", "account api"
  • PASS
    Free tier or no-card trial stated in textFree tier or no-card signals at https://postmarkapp.com/pricing: "No Credit Card", "Free Trial", "$0.00"

E · Integration

  • PASS
    Typed SDK on the registrypostmark@5.1.0 ships types
  • PASS
    Machine-readable API descriptionOpenAPI at https://postmarkapp.com/swagger/server.yml, which your docs page declares with rel="service-desc"

Tell me when this changes

The failures here are the kind nobody notices. An edge rule that starts refusing agents changes nothing a person sees in a browser, so the first sign is usually an integration that quietly stopped working. We rescan weekly and write only when a verdict moves.

This page is the newest scan we hold for postmarkapp.com and changes when we rescan. It is not a judgement of the product: we measure whether an unattended run can get through, not whether the thing is any good. The whole corpus is published as JSON and CSV.

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