Reverse DNS Lookup - PTR Checker by IP

Reverse DNS Lookup (PTR Checker)

Lookup PTR records for any IPv4 address and verify reverse DNS identity. Validate rDNS and forward-confirmed reverse DNS for email and network troubleshooting.

Purpose

IP to hostname mapping

Find PTR identity for a source IP quickly.

Best For

Mail deliverability diagnostics

Catch missing PTR and FCrDNS mismatches.

How This Helps

Reverse DNS is a core trust signal for sender reputation. Validate PTR first, then align SPF, DKIM, and DMARC for full authentication posture.

Common Uses

•SMTP troubleshooting: validate sender IP identity.

•Security reviews: classify unknown IPs in logs.

•Provider audits: verify custom PTR was applied.

•Reputation checks: reduce trust friction in receiving MTAs.

Use Reverse DNS Lookup (PTR Checker) in 4 Steps

Enter IP address

Type the public IPv4 address you want to inspect (e.g. 8.8.8.8).

Run PTR lookup

Press Lookup to query reverse DNS (in-addr.arpa) for PTR records.

Review hostname

Check the returned hostname and compare it with your expected server name.

Validate forward match

Confirm the hostname resolves back to the same IP (forward-confirmed rDNS).

What is Reverse DNS (rDNS)?

Reverse DNS maps an IP address to a hostname using PTR records. Standard DNS maps hostnames to IPs; reverse DNS performs the opposite lookup path.

Reverse lookups are widely used in email security, reputation checks, and network operations to verify that an IP has a trustworthy identity.

💡For best deliverability, keep your sending IP PTR aligned with your mail hostname and verify that the hostname resolves back to the same IP.

Why Reverse DNS Matters

Email trust: many receiving servers penalize or reject mail from IPs without valid PTR.
Abuse triage: identify host ownership quickly from logs and firewall events.
Provider validation: confirm dedicated IP assignments and custom PTR delegation.
Compliance posture: maintain consistent host identity across DNS and mail headers.

Forward-Confirmed Reverse DNS (FCrDNS)

FCrDNS means the PTR hostname resolves back to the same IP using an A/AAAA lookup. This is a common trust signal in mail pipelines.

Good state

IP → PTR hostname exists and hostname → A record points back to same IP.

Risk state

No PTR, generic PTR, or PTR hostname that does not map back to the source IP.

Who Controls PTR Records?

PTR records are usually controlled by the owner of the IP block (cloud provider, hosting provider, or ISP), not by your domain DNS zone.

If you use provider IPs, set custom PTR in provider networking settings.
If PTR is missing, request delegation or a reverse record update from the provider.
For shared IP pools, custom PTR may be unavailable without a dedicated IP.

Reverse DNS Troubleshooting Checklist

Check PTR exists: verify at least one PTR record is returned for the IP.
Validate hostname quality: avoid generic or malformed hostnames.
Confirm forward mapping: A/AAAA should return the same sending IP.
Align with SMTP identity: HELO/EHLO hostname should match PTR strategy.
Pair with SPF/DKIM/DMARC: DNS identity and email auth should be coherent.

CLI Verification

# Reverse lookup (PTR)

dig -x 8.8.8.8 +short

# Forward check on returned hostname

dig dns.google A +short

If reverse and forward lookups disagree, fix PTR or hostname mapping before troubleshooting application-level email issues.

Frequently Asked Questions

What is reverse DNS (rDNS)?

Reverse DNS maps an IP address to a hostname using a PTR record. It’s the opposite of normal DNS, which maps hostnames to IPs.

Why is reverse DNS important for email?

Many mail servers check that the sending IP has valid rDNS and that the hostname resolves back to the same IP (forward-confirmed rDNS). Missing or mismatched rDNS can hurt deliverability.

Where do I configure PTR records?

PTR records are usually managed by the owner of the IP block (your hosting provider, cloud provider, or ISP). They are not typically set in your domain’s DNS zone.

Can a single IP have multiple PTR records?

Technically it can, but many email providers expect a single consistent PTR. For mail servers, a single PTR that matches your HELO/EHLO hostname is best practice.

Why does rDNS show a hostname I don’t control?

If you are using a shared server or a provider-managed IP, the PTR may be set to a provider hostname. You may need a dedicated IP or request a custom PTR from the provider.

Related Tools

DNS Lookup

Validate A, AAAA, MX, TXT, NS and SOA records.

NS Lookup

Check domain authority and nameserver ownership.

SPF Checker

Validate SPF policy for sending domains.

DMARC Checker

Validate DMARC policy and reporting alignment.