# Reverse DNS (PTR) Lookup URL: https://iblockspam.com/tools/ptr-lookup Last updated: 2026-10-09 > Check that a mail server's IP address has a PTR record, that the name points back to the same address, and that it doesn't look like a generic consumer connection. Free tool: Check PTR records, forward-confirmed reverse DNS and generic-looking host names. Use it at https://iblockspam.com/tools/ptr-lookup ## What the Reverse DNS Lookup checks Receiving mail servers look at the IP address that connected to them and ask DNS for its name. This tool runs the same checks: - **PTR record.** Does the address have a reverse DNS name? - **Forward confirmation (FCrDNS).** Does that name have an A record (or AAAA for IPv6) that points back to the same address? - **Generic name (heuristic).** Does the name look like an auto-generated one, such as `203-0-113-10.dyn.example.net`? Enter an IPv4 or IPv6 address, or a domain. For a domain we look up its MX records and check up to four mail server addresses. Private and reserved addresses are refused. ## How to read the results - **Pass.** A PTR exists, and its name resolves back to the address. - **Warning.** The name looks generic. Some receivers score that as a likely consumer or unmanaged host. - **Fail.** There is no PTR, or the name doesn't resolve back to the address. - **Not tested.** A lookup timed out. Try again. ## Why reverse DNS matters for email [Google's email sender guidelines](https://support.google.com/mail/answer/81126) say that all senders must have valid forward and reverse DNS for their sending IPs, and that the public IP of a sending server must have a PTR record that resolves to a host name. Many other receivers reject or score down mail from addresses with no PTR, or with a PTR that doesn't match. The PTR name doesn't have to be in the same domain as your From address. It should be a stable name for the server, such as `mail.yourcompany.com` or your mail provider's own host name, and it should match the name the server uses in its SMTP greeting. ## Common problems and fixes **No PTR record.** Open a ticket with your hosting provider or ISP, or use the reverse DNS setting in your cloud console. You can't add a PTR in your own domain's DNS zone. **PTR doesn't resolve back.** If the PTR is `mail.yourcompany.com`, add an A record for `mail.yourcompany.com` pointing to the same IP. Or change the PTR to a name that already does. **Generic name.** Ask the provider to replace the default name with your mail server's name, then add the matching A record. **You use Microsoft 365 or Google Workspace.** Their sending servers already have correct reverse DNS. You only need to manage PTR records for servers you run yourself, such as an on-premises Exchange server or a relay. ## Limitations - For a domain we check inbound mail servers from its MX records. The servers that send your mail may be different. Enter their IP addresses to check them directly. - We check up to two PTR names per address. - The generic-name check is a pattern match. A name like `static-203-0-113-10.example.net` may belong to a perfectly managed server. ## Related Check the same addresses against spam blocklists with the [Blacklist Checker](https://iblockspam.com/tools/blacklist-checker), or read the [Gmail, Yahoo and Microsoft sender requirements](https://iblockspam.com/blog/gmail-yahoo-microsoft-bulk-sender-requirements). ## Frequently asked questions ### What is a PTR record? A PTR record maps an IP address back to a host name. It lives in a special reverse zone, such as 10.113.0.203.in-addr.arpa for 203.0.113.10, which is controlled by whoever owns the IP range: your hosting provider or ISP, not your domain's DNS host. ### What is forward-confirmed reverse DNS (FCrDNS)? It means the PTR name for an IP address resolves back to that same address. Receiving mail servers check this because anyone can make their own domain point at any IP, but only the owner of the IP range can set its PTR record. ### Does Gmail require reverse DNS? Yes. Google's email sender guidelines require all senders to have valid forward and reverse DNS for their sending IPs, and say the public IP of a sending server must have a PTR record that resolves to a host name. ### How do I change my PTR record? Ask whoever controls the IP address. For a cloud or VPS server it's usually a setting in the provider's control panel. For a business internet line, ask your ISP. You can't set it in your own domain's DNS zone. ### What makes a PTR name look generic? Names that contain the IP address, words such as dynamic, dhcp, pool or dsl, or a cloud provider's default name. They suggest an unmanaged or consumer connection. Our check is a pattern match, so treat it as a hint, not a verdict. --- Source: iBlockSpam, https://iblockspam.com/tools/ptr-lookup (this is a Markdown copy; the HTML page is canonical). Quote with attribution and a link. Site index for AI assistants: https://iblockspam.com/llms.txt