Let Agents In

Agent readiness · postmarkapp.com

2026-08-12 10:27 UTC · formula v9.2 · 19.6s

A recaptcha challenge sits between an agent and an account it was ready to create.

https://account.postmarkapp.com/sign_up loads recaptcha. There is no version of that an agent solves.

8/ 12
A · Discovery
5/5
B · Agent entry
0/2
C · Registration
1/2
D · Provisioning
1/1
E · Integration
1/2

of the 12 points that apply to you and we could measure · 5 of 17 were not scored

You 8 · category median 10.5 · best resend.com 14 · 15 deterministic HTTP checks, published formula

Pass it onEmail itLinkedIn

Fix this first

+2points, taking 8/12 to 10/12, past mailgun.com, sendgrid.com

This is the whole list: everything we could measure and you do not pass. Another 5 points sit behind checks we could not evaluate on your domain, and each of those lines below says what would make it measurable.

  1. 1
    No CAPTCHA in the signup HTMLan afternoon · +1

    Trigger recaptcha on a risk signal instead of on every signup, or open an API path to an account. A CAPTCHA is a hard stop, not a speed bump.

  2. 2
    Machine-readable API descriptionan afternoon · +1

    Publish an OpenAPI file at /openapi.json, or serve markdown when a client sends Accept: text/markdown. Either one stops agents guessing your API.

Then, when you have room

  • OAuth dynamic client registration a project · +1Publish OAuth authorization server metadata with an RFC 7591 registration_endpoint in it. It is the only standard way an agent registers itself without a human.
  • MCP surface a project · +1Wrap your top three API calls in an MCP server and declare it at /.well-known/mcp.json.

Take it with you

5 of the checks an agent depends on, postmarkapp.com does not pass.

Send yourself the list above with the checks that cost the most, and a permanent link. Whoever owns the fix is usually not the person who ran the scan.

One email with the report, and one follow-up asking what you did with it. No newsletter, no sequence. Delete on request at hello@letagentsin.com.

None of this tells you whether an agent picked you

Everything above is a file an agent could read. Whether one actually chose you is a different measurement, and we have not run it on postmarkapp.com. What we have run it on is a rich text editor vendor: six agents, one brief, six isolated copies of a real codebase. All six picked the same competitor, and the vendor being studied was never named, not even on a rejection list, while the runs named and dismissed ten alternatives between them. In an earlier round, run before we isolated the copies, it was named twice and struck off both times in four words: Fully commercial, licence key required. That study is about them, not about you. It is here because it is the difference between a file and a decision.

Read the audits in fullWhat the same run on postmarkapp.com costs

Against transactional email apis

You are 4 of 6 in a category where a developer is trying to send password resets and receipts that arrive.

  1. 1
    resend.com
    14/16
  2. 2
    loops.so
    13/16
  3. 3
    sendlayer.com
    12/16
  4. 4
    postmarkapp.comyou
    8/12
  5. 5
    mailgun.com
    9/14
  6. 6
    sendgrid.com
    9/14

Where competitors pass and postmarkapp.com does not

  • Machine-readable API descriptionresend.com · sendgrid.com · mailgun.com · loops.so · sendlayer.com
  • MCP surfaceresend.com · loops.so · sendlayer.com
  • No CAPTCHA in the signup HTMLresend.com · loops.so · sendlayer.com
  • OAuth dynamic client registrationresend.com

Only domains we have actually scanned appear here, so the ranking is a floor: a competitor missing from the list has not been measured, not beaten.

By stage

A
DiscoveryCan an agent find and read you?
5/5
B
Agent entryIs there a door built for a machine?
0/2
C
RegistrationCan an agent get an account?
1/2
D
ProvisioningCan it get credentials without a human?
1/1
E
IntegrationCan it ship working code?
1/2

Every check

Each line is one HTTP observation with a published rule, so you can rerun any of them yourself. Most are the same tomorrow if you are: the two that are not are the bot gate and the pricing page, which answer inconsistently on their own, which is why those run more than once and say so when the tries disagreed. PASS and PART are counted. UNMEASURED means we could not evaluate it, N/A means it does not apply to a product like yours, and neither is in the score or its denominator. See the formula

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: 3 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 subdomainsRFC 7591 is the only standard path by which an agent can register itself without a human.
  • 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 MCPAn MCP server turns your API from something an agent reads about into something it can call.

C · Registration

  • FAIL
    No CAPTCHA in the signup HTMLrecaptcha appears in the signup page's server HTMLA CAPTCHA is a hard stop. Permissions after signup beat a gate before it.
  • PASS
    Signup reachable without a browserForm renders in server HTML at https://account.postmarkapp.com/sign_up

D · Provisioning

  • UNMEASURED
    Programmatic key provisioningUnmeasurable: 1 documentation page we selected did not answer (429, and a 429 is our own burst rather than an answer about agents), so nothing here is a finding about what you documentLet ordinary HTTP reach your documentation pages and this becomes measurable.
  • 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
  • FAIL
    Machine-readable API descriptionNo OpenAPI spec at the 5 usual paths, none declared by https://postmarkapp.com/developer, and no markdown negotiationAn OpenAPI file or markdown negotiation lets an agent read your API instead of guessing it.Point at your spec from your docs page with rel="service-desc" and an agent finds it without guessing.

What we discovered on the way

Docs
https://postmarkapp.com/developer · linked from the site
Pricing
https://postmarkapp.com/pricing · linked from the site
Signup
https://account.postmarkapp.com/sign_up · linked from the site
npm package
postmark
GitHub
not found
Package licence
MIT
Crawl-delay
none
Content-Signal
none
Blocked on-demand agents
none

The signup page answered inconsistently across three tries (200, 0, 200). Bot gates do that, and an agent hitting the wrong try simply leaves.