IP address to hostname
DNS & Records
DNS Lookup Every DNS record for any domain A Record Lookup IPv4 addresses for a domain AAAA Record Lookup IPv6 addresses for a domain MX Lookup Mail servers for a domain NS Lookup Authoritative name servers TXT Lookup TXT records, SPF, verification CNAME Lookup Canonical name (alias) records SOA Lookup Start of Authority record SRV Lookup Service location records CAA Lookup Which CAs may issue certificates Reverse DNS (PTR) IP address to hostname DNSSEC Check Is the domain signed and validated? DNS Health Check A full delegation & DNS report cardEmail Deliverability
SPF Check Validate your Sender Policy Framework record DMARC Check Inspect and grade your DMARC policy DKIM Check Find and validate your DKIM public key Blacklist Check Check an IP against email blocklists (DNSBLs) SMTP Test Connect to a mail server and check STARTTLS MTA-STS Check Enforced TLS policy for inbound mail BIMI Check Brand logo record for email TLS-RPT Check SMTP TLS reporting policyNetwork & Web
SSL Certificate Check Inspect a site's TLS certificate and expiry HTTP Header Check Inspect response headers, redirects and security Ping (TCP) Reachability and latency over TCP Port Check Which common ports are openDomain
WHOIS Lookup Registration data for domains, IPs and ASNsReverse DNS resolves an IP address back to a hostname through a PTR record, the opposite of a normal forward lookup. Mail servers check it to gauge sender reputation, so a missing or generic PTR record can hurt email deliverability. PTR records live in the special in-addr.arpa and ip6.arpa zones managed by whoever controls the IP block.
A PTR record maps an IP address to a hostname, the reverse of an A record. The IP is queried as a name in a special zone: 93.184.216.34 becomes 34.216.184.93.in-addr.arpa, and IPv6 uses ip6.arpa. Critically, PTR records are controlled by whoever owns the IP block, usually your hosting provider or ISP, not by your domain's DNS. To set or change one, you request it from them rather than editing your own zone file.
Receiving mail servers run a reverse DNS lookup on a connecting IP to judge whether it is a legitimate mail source. A clean setup has the PTR resolve to a real hostname (mail.example.com) whose forward A record points back to the same IP, called forward-confirmed reverse DNS (FCrDNS). A missing PTR, or a generic one like a string of digits in a broadband provider's domain, signals a residential or unconfigured host and often triggers spam filtering or outright rejection. Proper PTR is essential for any server sending email.
A PTR result shows the hostname an IP resolves to, for example 34.216.184.93 PTR mail.example.com. Confirm it is FCrDNS-valid by checking that mail.example.com has an A record returning the same IP. If the lookup returns nothing, no PTR is set; if it returns a generic provider hostname, the default is still in place. Fix either by asking your hosting provider or ISP to set the PTR to a hostname you control, then publish a matching forward A record so the two agree.
A PTR record is a DNS record that maps an IP address back to a hostname, enabling reverse DNS lookups, the opposite of an A record. PTR stands for pointer. It lives in the in-addr.arpa zone for IPv4 or ip6.arpa for IPv6, and is controlled by the owner of the IP block, typically your hosting provider or ISP.
A PTR record is important for email because receiving mail servers check it to verify a sending IP belongs to a legitimate, properly configured host. A missing or generic PTR makes your mail look like it comes from a residential or unconfigured source, which commonly triggers spam filtering or rejection. A matching PTR and forward record build sender reputation and improve deliverability.
You set up a PTR record by requesting it from whoever owns the IP address, usually your hosting provider or ISP, since PTR records live in their reverse zone, not your domain's DNS. Ask them to point the IP at a hostname you control, then publish a matching A record for that hostname so forward and reverse lookups agree (FCrDNS).
Forward DNS resolves a hostname to an IP address using A or AAAA records, while reverse DNS resolves an IP address back to a hostname using a PTR record. Forward lookups are what browsers do to reach a site; reverse lookups are mainly used by mail servers and logging tools to identify and verify the host behind an IP.
Your PTR record may not match your domain because the IP owner left its default generic hostname in place, or set a PTR you did not request a change to. PTR records are managed by your hosting provider or ISP, not your own DNS, so a mismatch means their reverse zone needs updating. Request the correct hostname and add a matching forward A record.