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Lookproof PTR / FCrDNS Mail Server Check
x402
Lookproof PTR / FCrDNS Mail Server Check is a paid API for AI agents from api.lookproof.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-31).
Checks reverse DNS (PTR records) for a domain's MX hosts and validates full-circle reverse DNS (FCrDNS) for each mail server IP address
Price / call$0.01
Success—
StatusUnknown
How this service works
Check SPF, DMARC, DKIM, MTA-STS, DNSSEC and more, with results that explain what was found and why. Free browser checks and a pay-per-request API with x402.
Output
Returns up to five MX hosts for the domain, each with their resolved IPv4 and IPv6 addresses, the PTR name found for each address, whether that PTR resolves back to the same IP (FCrDNS pass/fail), and coded diagnostic findings indicating configuration problems.
Example use cases
Diagnose rejected outbound email
“Our emails from sendgrid.acme.com keep getting rejected by recipients. Can you check if the mail servers for acme.com have valid PTR records and whether they pass the full-circle reverse DNS check?”
Pre-launch mail server audit
“Before we go live, can you verify that all the MX hosts for newstartup.io have matching reverse DNS on both IPv4 and IPv6? I need to know which ones pass FCrDNS and which ones might cause deliverability issues.”
Spam folder investigation
“A client is complaining that emails from mybusiness.com land in spam. Can you look up the reverse DNS for all their mail server IPs and tell me if any of the PTR records don't match back to the same address?”
Technical details
Endpoint
GEThttps://api.lookproof.dev/v1/mail/ptr?utm_source=zero.xyzWhen to prefer
Use this endpoint when you specifically need to diagnose reverse DNS configuration for a domain's mail servers, especially when troubleshooting email rejection or spam-filing caused by missing or mismatched PTR records. Prefer this over generic DNS tools when you need FCrDNS validation (PTR resolves back to the original IP) across all MX hosts in a single call.
Side effects
- Domain does not exist or has no MX records — returns empty or error result
- Domain has more than five MX hosts — only up to five are checked
- PTR lookup fails due to no reverse DNS zone configured — reported as missing PTR
- Network timeout resolving IPv4 or IPv6 addresses — partial results may be returned
- Invalid domain format provided — returns validation error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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