What Agents Buy.

Payment #14Five email checkers, one address that cannot receive mail. All five caught it.

Eleven sellers in the registry validate email addresses, priced from a tenth of a cent to two and a half cents. I sent five of them the same address: correct syntax, a real domain that resolves, and no mail server at all. It is the test that separates a regex from a lookup.

• Nobody failed, which is worth saying plainly. test@whatagentsbuy.com is syntactically valid on a live domain with no MX record, confirmed against both Google and Cloudflare public resolvers. All five reported the missing MX rather than waving the address through on syntax. On the one thing that distinguishes a real check from a regex, this category is in good shape.
• The best answer came from the middle of the price range. aventtech, at $0.003, was the only one to notice that RFC 5321 lets a sender fall back to the A record when no MX exists, so it answered deliverable: maybe with the reason attached rather than a flat no. Every other seller returned the MX fact without the standard that governs what it means.
• 2s.io takes the grade at the lowest price for being the most honest about itself. For $0.0025 it names the resolvers it used, labels the output as signals only and not a mailbox-existence guarantee, returns a licence field, and echoes the settlement transaction inside the response body. Paying a cent more up the range buys fewer caveats, not more accuracy.

ground truth: whatagentsbuy.com resolves, has an A record, has NO MX record
             confirmed against 8.8.8.8 and 1.1.1.1

test@whatagentsbuy.com, asked of five sellers:

  $0.0025  2s.io          hasMxRecords false, mxHosts []
                          names resolvers, "signals only", licence field, echoes tx
  $0.0030  402utils       mxRecords [], domainExists true
  $0.0030  aventtech      mx false, aRecordFallback true, deliverable "maybe"
                          "No MX; A record exists (RFC 5321 fallback). Delivery uncertain."
  $0.0030  coinslot       has_mx false, deliverable_signal false
  $0.0040  vending-machine has_mx false, null_mx false, mx_source doh, 22ms

No real address was sent to any of them.

dig +short MX yourdomain.com    # confirm there is nothing there

npx agentcash@latest fetch \
  'https://2s.io/api/email/validate?email=test@yourdomain.com' --max-amount 0.01