{"uid":"cap_jVtPdU0ekSdDAFFYZmtM5","slug":"probekit-mail-ptr-fcrdns-check-bd3356ed","name":"ProbeKit Mail PTR / FCrDNS Check","description":"Check reverse DNS for a domain's mail servers: up to five MX hosts, their IPv4 and IPv6 addresses, each PTR name and whether it resolves back to the same address (FCrDNS), with coded findings. Use when an agent must tell whether a domain's mail servers have matching reverse DNS, a common reason for rejected or spam-filed mail.","url":"https://api.probekit.dev/v1/mail/ptr?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET","HEAD","DELETE"],"type":"string"},"queryParams":{"type":"object","title":"DomainInput","required":["domain"],"properties":{"domain":{"type":"string","title":"Domain","examples":["example.com"],"maxLength":1024,"minLength":1}},"additionalProperties":false}},"additionalProperties":false}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.01","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.01/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_vecO1pLrUAB4OhFVbqilk","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.01","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Checks reverse DNS (PTR records) for a domain's MX hosts and validates forward-confirmed reverse DNS (FCrDNS), flagging mismatches that cause mail rejection or spam filtering.","exampleAgentPrompt":"Check whether acme.com's mail servers have proper reverse DNS — I need to know if each MX host has a PTR record that resolves back to the same address (FCrDNS), because our outbound email keeps getting flagged as spam.","exampleUseCases":[{"title":"Diagnosing rejected outbound email","prompt":"Our emails from startupco.io keep bouncing with a reverse DNS error — can you check if the MX servers for startupco.io have valid PTR records and whether they pass FCrDNS?"},{"title":"Pre-send deliverability audit","prompt":"Before we launch our email campaign, can you verify that all the mail servers for newsletterco.com have matching forward and reverse DNS so our messages don't land in spam?"},{"title":"Monitoring client mail server rDNS","prompt":"Check the reverse DNS setup for clientdomain.net's mail servers and tell me which MX hosts are missing PTR records or failing FCrDNS validation."}],"resultDescription":"Returns up to five MX hosts for the domain, each with their resolved IPv4 and IPv6 addresses, the PTR (reverse DNS) name for each address, a boolean or status indicating whether FCrDNS passes (PTR resolves back to the same IP), and coded findings summarizing any issues detected.","failureModes":["Domain does not exist or has no MX records — returns empty or error result","MX host is unreachable or DNS lookup times out — partial results with timeout indicator","Domain input exceeds 1024 characters or is empty — validation error","PTR record exists but forward resolution returns different IP — FCrDNS failure flagged in findings","Network or resolver error preventing reverse DNS lookup — coded error finding returned"],"whenToPreferThis":"Choose this endpoint when you specifically need to audit reverse DNS and FCrDNS correctness for a domain's mail servers, especially when diagnosing email rejection or spam-folder placement caused by PTR mismatches. It focuses solely on PTR/FCrDNS analysis rather than full mail configuration (SPF, DMARC, DKIM), making it the right choice for targeted rDNS troubleshooting rather than a broad mail health check.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-30T19:06:07.245Z","isFirstParty":false,"canonicalSlug":"probekit-mail-ptr-fcrdns-check-bd3356ed"}