AltF DomainOps

Reverse DNS (PTR) lookup and IP owner

Reverse DNS turns an IP address back into a hostname using its PTR record. DomainOps builds the in-addr.arpa or ip6.arpa name, looks it up, then checks that the hostname points back to the same IP (forward-confirmed reverse DNS), and asks the regional registry who the network is allocated to.

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Why reverse DNS matters for email

Receiving mail servers check the PTR of the connecting IP. A missing PTR, or one that does not resolve back to the same IP, is a common reason mail from a self-hosted server is rejected or sent to spam. PTR records are set by whoever owns the IP block, usually your hosting or cloud provider, not in your own DNS zone.

What the owner lookup shows

The network name, address range and organisation the regional internet registry (ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC) has on file for the block. That is usually an ISP or cloud provider, not the person using the address.

Reverse DNS lookup: questions and answers

How do I set a PTR record?

In your hosting or cloud provider's panel, usually under networking or the server's IP settings. Cloud providers such as AWS, Google Cloud and DigitalOcean let you set it for addresses you hold; home ISPs usually do not.

Can reverse DNS find every website on an IP?

No. A PTR record holds one name. Shared hosting can serve thousands of sites from one IP without any of them appearing in reverse DNS.

Focused checks and guides

Checks

Full domain health checkAll nine tools, the record glossary and how each check works.DNS lookupFree DNS lookup for A, AAAA, CNAME, MX, NS, TXT, SOA, CAA, SRV, DS, DNSKEY and HTTPS records, with TTLs, DNSSEC status and what each record means.MX lookupFree MX record lookup: see a domain's mail servers in priority order, which email provider runs them, and whether SPF and DMARC are set.NS lookupFree nameserver lookup: see which nameservers answer for a domain, who the DNS host is, the SOA serial, and whether the zone is DNSSEC-signed.TXT record lookupFree TXT record lookup that labels each record: SPF, Google and Microsoft verification, Meta, Apple, Stripe and 25 more services, plus DMARC and DKIM.SSL certificate checkFree live SSL checker: connect to any site and see its certificate issuer, expiry date and days left, covered hostnames, chain trust and TLS version.Domain expiry checkCheck when a domain expires from the registry's own RDAP data: expiry date, days left, registrar, transfer lock and status codes in plain English.DNSSEC checkCheck whether a domain uses DNSSEC: DS record at the registry, DNSKEY in the zone and whether public resolvers validate the answers.CAA record checkLook up a domain's CAA records to see which certificate authorities may issue certificates, including wildcard and reporting rules, with fixes.

Guides

Domain launch checklistA 20-point checklist to launch a new domain: DNS records, www, HTTPS, email authentication, DNSSEC, CAA, registrar lock, with a free check for each step.Website migration DNS checklistMove a website or DNS to a new host without downtime: lower TTLs, copy records, switch nameservers, watch resolvers, handle DNSSEC and email.Email domain setup guideSet up email for your domain the right way: MX records, one SPF record under 10 lookups, DKIM keys, a DMARC rollout plan, MTA-STS and BIMI.

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AltFTool does not store the domains or addresses you check. DNS lookups in the DNS, compare, email and IP tools run from your browser; registration, report and certificate checks pass through AltFTool's server and keep nothing.