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ProbeKit Mail PTR / FCrDNS Check
x402
ProbeKit Mail PTR / FCrDNS Check is a paid API for AI agents from api.probekit.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-30).
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.
Price / call$0.01
Success—
StatusUnknown
How this service works
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.
Output
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.
Example use cases
Diagnosing rejected outbound email
“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?”
Pre-send deliverability audit
“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?”
Monitoring client mail server rDNS
“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.”
Technical details
Endpoint
GEThttps://api.probekit.dev/v1/mail/ptr?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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