How To Reverse Look up DNS (rDNS)

Updated on May 14th, 2022
by Editorial Team

The domain name system, sometimes known as DNS, is an essential component of the internet. It is so important that using the internet without DNS would be far too difficult. DNS is a recursive directory system that manages all of the Internet's website addresses. In some instances, it may be necessary to reverse the DNS. To determine the domain address or hostname for a specific IP address, for example. A reverse DNS (rDNS) or reverse domain lookup is what this is. In this article we will learn how to reverse look up dns.

Email spam is frequently filtered using reverse DNS requests (also using DMARC). Spammers can easily change the sending email address to any domain name they desire, including reputable ones like banks or trustworthy businesses.

What is reverse DNS (rDNS)?

Reverse DNS (rDNS) is a type of name resolution that looks up IP addresses to get a domain name, rather than the DNS server's job of converting domain names to IP addresses.

rDNS is a DNS lookup of a domain name from an IP address. rDNS resolves a domain name to an IP address, but regular DNS does the opposite, hence the term reverse. For rDNS lookups, PTR records are used. If no PTR record is specified, a rDNS lookup fails.

Humans, unlike robots, have a difficult time reading and remembering numeric IP addresses. This is why we visit websites using domain names. Reverse DNS converts complex website visit logs into readable domains, making data collection for analytics easier.

Reverse DNS can be used to filter spam. Spammers frequently utilize invalid IP addresses, or addresses that do not match domain names. When a reverse DNS program checks up an incoming message's IP address and finds no legitimate domain name, the server stops the message. Although rDNS is good at filtering spam, it frequently prevents legitimate emails.

How does reverse DNS (rDNS) work?

The domain name and the IP address assigned to the website's server can be used to access most websites on the internet. You can get to a website's homepage by typing the IP address xx.xx.xx.xx into your browser's address bar. You can access the site by typing its IP address directly into your browser because its domain has a valid rDNS.

PTR records link IPv4 or IPv6 addresses to canonical host names when rDNS lookups are conducted. The lookup, however, fails if the web server does not have a pointer record set up.

PTR records are used to store rDNS entries that have their IP addresses reversed and the suffix.in-addr.arpa appended to each record. The IP address xx.xx.xx.xx.in-addr.arpa, for example, is recorded by PTR as xx.xx.xx.xx.in-addr.arpa, which leads back to the assigned host name.

By typing the IP address of a domain name with a valid rDNS into your browser, you can go to it.

When running an SMTP/mail server, it is critical to set up a proper rDNS record (PTR).

What are the objectives of reverse DNS server?

For folks who run an outgoing mail server, Reverse DNS is quite useful. There are several other reasons to utilise rDNS besides mail servers:

  • Spam email filtering: To combat spam, most email servers utilise rDNS to reject messages from IP addresses that do not have rDNS. However, due to the fact that certain legitimate mail servers do not have properly set rDNS records, rDNS is usually utilised as an additional layer of protection.
  • A pleasurable network encounter: Reverse DNS has little effect on most corporate administration systems, r-commands, SMTP servers, or network backup solutions. rDNS is also required for the operation of a number of Internet protocols.
  • Safeguarding: A reverse IP lookup can be used to find the A records for an IP address, which connect a domain name to the IP address of the device that hosts it. The findings help uncover server faults and determine which virtual hosts are served by a web server.
  • Analytics: Reverse DNS assists in giving human-readable data in analytics instead of posting logs of IP addresses.
  • Keeping track of website visitors: IP addresses are recorded in visit logs and can help you figure out who is visiting your site. Keeping track of website visitors might help you generate B2B leads.

Reverse DNS and spam filtering

Spam filtering is the most prevalent and important rDNS function. The recipient's mail server runs a rDNS query to see if the sender's mail server is valid once a fresh email enters the anti-spam security gateway. The incoming message is automatically discarded if it does not return a valid rDNS record.

That's why it's critical to set up PTR records on your mail servers, both to prevent spam and to ensure that messages go to their intended recipients.

Also read: Achieve 10/10 Email score with CyberPanel!

How to reverse look up dns?

Reverse DNS lookup can be done in a variety of ways:

  1. Use the command prompt in Windows. Using the nslookup command in Windows, perform a manual rDNS lookup.
  2. Use the Linux terminal to get started. You can execute manual rDNS lookups using the dig command with the -x parameter. You can also use the host command.
  3. Use lookup tools for rDNS records. rDNS lookup is available through a number of tools.

For windows:

In Windows, the reverse DNS lookup command is:

nslookup [ip address] 

For, example:

how to reverse look up dns

As we can see, dns.google is the reverse DNS of the IP we had given.


The "dig" command is used to search for information. Use the dig command in Linux to perform a manual reverse DNS lookup. The following is the syntax:

dig -x [ip_address]

reverse DNS

"host" is a command. You may also run a reverse DNS query in Linux with the following command:

 host [ip_address]

Lookup tools

You can lookup a limited number of IP addresses using online reverse DNS tools. Some may also offer an API for business applications.

mxToolBox is one of these tools. Simply enter your IP in there to find the rDNS.

How to set rDNS in Vultr

  • Login and select the VPS for which you want to set rDNS for
  • Click on settings
  • Click on rDNS
  • Edit rDNS and click the tick mark to save
  • Your DNS has been set

How to set rDNS in Hetzner

  • Login to your Hetzner account
  • Enter your project
  • Click on the VPS for which you want to create rDNS for and click on "Networking" from the left hand side menu
  • Click on options and select "Edit Reverse DNS"
  • Edit your rDNS and click "Edit Reverse DNS"

you have succefully set rDNS in Hetzner

How to issue mail server SSL against the domain for which you want to create rDNS for in CyberPanel?

  • Login to your CyberPanel account and select SSL -> Mail Server SSL from the left hand side menu
  • Select your domain. If your issuing SSL for mail sever against that domain, then your rDNS should also be same as the domain

Now mail server's host name will be this domain name. So when ever you send an email, this domain name will appear.


The most efficient technique to link a single IP address itself to domain name is to use reverse DNS lookup. The process, however, can only be completed after the ISP provider has pointed the zone to the IP's DNS server system. The PTR record then becomes available for reverse DNS entries, which can map IPv4 or IPv6 addresses to the host's canonical name.

In order to obtain vital information and produce B2B leads, reverse DNS lookup is most typically used to filter spam emails and identify website visitors' domains. You may manually discover the domain of any IP address by performing a reverse lookup. Despite this, if you need to run hundreds of reverse DNS lookups, the procedure may get laborious.

One comment on “How To Reverse Look up DNS (rDNS)”

  1. Apr 27 01:08:16 empresas postfix/smtpd[311942]: disconnect from unknown[---.---.---.---] ehlo=1 auth=0/1 rset=1 quit=1 commands=3/4
    Apr 27 01:08:18 empresas postfix/smtpd[312315]: connect from unknown[---.---.---.---]

    ---.---.---.--- = Hided my IP

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