Look up PTR records: IP address to hostname.
Reverse DNS (PTR) maps an IP address back to a hostname. Authoritative PTR records live in the reverse zone (e.g. in-addr.arpa for IPv4, ip6.arpa for IPv6), usually managed by the party that owns the IP block (ISP or hosting provider). This tool performs a PTR lookup for a given IP and shows the resulting hostname(s). Use it to verify that your server's reverse DNS is set correctly (important for email deliverability and SSH), to identify the owner of an IP, or to debug connectivity and logging. Not all IPs have PTR records; missing or wrong PTR can cause mail to be marked as spam.
Many mail servers check that the sending IP has a PTR that matches or relates to the sending domain; missing or mismatched PTR can trigger spam filters.
Only if you control the reverse zone. Usually your ISP or host sets PTR for your IP; ask them to point it to your hostname.
No PTR record is configured for that IP. The owner of the IP block must add it.
Best practice is for the PTR hostname to resolve back to the same IP (forward-confirmed reverse DNS).
PTR for IPv6 uses ip6.arpa. Your provider must add the record in the delegated reverse zone.