反向DNS查詢（PTR）
透過PTR記錄查詢與任意IP位址關聯的主機名稱。
如何使用本工具
- 1
Type or paste an IP address into the input box, for example 8.8.8.8 or an IPv6 address like 2001:4860:4860::8888.
- 2
Click Lookup to send the address to our server, which runs a reverse DNS (PTR) query against the public DNS system.
- 3
Read the returned hostnames in the results list, or the 'No PTR record found' notice if the address has no PTR record or the lookup fails.
- 4
Try another address to compare results, for example a mail server IP versus a residential or cloud IP.
什麼是反向DNS查詢（PTR）？
正向DNS將主機名稱對應到IP（example.com → 1.2.3.4）。反向DNS則相反：它透過PTR記錄詢問「哪個主機名稱擁有這個IP？」。這對郵件投遞至關重要：沒有PTR記錄的郵件伺服器常常會被大型供應商（Gmail、Microsoft）當作疑似垃圾郵件來源而拒收。
常見使用場景
Confirm a sending mail server's IP has a valid PTR record before going live, since Gmail and Microsoft 365 often reject or junk mail from IPs with no reverse DNS.
Read web server or firewall access logs and turn raw IP addresses into hostnames to spot which networks or providers are connecting.
Verify that a cloud or VPS provider correctly applied the custom PTR record you requested for an outbound IP.
Investigate a suspicious IP during incident response to see whether it points back to a known ISP, hosting company, or CDN.
Sanity-check a newly delegated IP block by confirming PTR records resolve as expected after a network migration.
Troubleshoot SSH or service connections where the daemon does a reverse lookup on the client IP and a missing PTR causes slow or failed logins.