Building Sender Reputation: The Role of Reverse DNS Lookup

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A reverse DNS lookup is the process of finding the domain name associated with an IP address, essentially the opposite of a regular DNS lookup.

But what does it have to do with email marketing

When you send an email campaign, recipient mail servers use reverse DNS to check the sending IP address’s legitimacy, helping ensure your emails land in inboxes and not spam folders. 

In short — if you want to prevent your emails from getting nuked by the spam filter, you should care about how this technical feature can make you appear as a genuine email sender.

Join us as we examine reverse DNS lookups and help you prep your email setup to appear authentic to mailbox providers.

What is DNS?

DNS stands for Domain Name System. It’s a decentralized, hierarchical naming system for computers, services, or any resource connected to the Internet or a private network.

DNS translates human-readable website names (like campaignrefinery.com) into machine-readable IP addresses that computers understand. So, when you type a website into your browser, DNS does the behind-the-scenes work of finding the corresponding IP address and directing your computer to the right website.

DNS makes the internet much easier to navigate by replacing complex IP addresses with memorable website names. DNS also helps speed up the process of finding websites by caching frequently accessed lookups.

DNS Records Explained

A DNS record is a data entry in the DNS database that provides information about a specific aspect of a domain name. These records contain various types of information used to translate domain names into IP addresses and vice versa. Each DNS record type serves a specific purpose in the DNS resolution process.

Common types of DNS records include:

DNS recordWhat they do
MX Record/Mail Exchange RecordThis record specifies the mail server responsible for receiving email for a domain.
A Record/Address RecordA DNS record that maps a domain name to an IPv4 address.
PTR/Pointer RecordUsed in reverse DNS lookups to map IP addresses to domain names.
NS Record/Name Server RecordStates the authoritative name servers for a domain.
SPF Record/Sender Policy Framework RecordSPF records specify which IP addresses are authorized to send emails on behalf of a domain.
DKIM Record/DomainKeys Identified Mail RecordContains a public key used to verify the authenticity of DKIM-signed emails.
Types of DNS Records Explained

Are you curious to know how each of these plays a role in an email reaching the inbox? In the next section, we delve into the technicalities.

How DNS Contributes to Email Running Smoothly

DNS records play a critical role in email communication by providing essential information for email delivery, authentication, and reputation management. 

DNS Records in Action

These DNS records contribute to email functionality:

  1. MX records,
  2. A records,
  3. PTR records,
  4. SPF and DKIM records.

Let’s check out how these DNS records help emails work as intended.

MX Records

“MX records” specify the mail servers responsible for receiving email on behalf of an email domain. When someone sends an email to an address such as “user@campaignrefinery.com,” the sender’s email server queries the DNS to find the MX records for “campaignrefinery.com.” 

These MX records point to the servers that will accept incoming emails for that domain. Without proper MX records, email delivery to the domain may fail.

“A” Records

“A records” map domain names to IP addresses. While MX records handle incoming email routing, A records can be essential for outbound email delivery. 

Email servers may perform reverse lookups on the IP address they are sending from to ensure it matches the domain name in the email’s “From” address. “A” records help establish this correspondence.

PTR Records

“PTR records” are used for reverse DNS lookups, matching IP addresses to domain names. They are crucial for authentication mechanisms such as SPF and DKIM. 

When an email server receives a message, it may check if the sender’s IP address has a PTR record that corresponds to the domain specified in the sender’s email address. A properly configured PTR record enhances email deliverability by confirming authenticity.


While SPF records specify which IP addresses are authorized to send emails on behalf of a domain, DKIM adds a digital signature to outgoing emails to verify their authenticity. We’ll explore both shortly.

What is a Reverse DNS Lookup?

To understand a DNS reverse lookup, you have to know what a regular DNS lookup does.

DNS Lookup

In a regular or forward DNS lookup, you enter a website address (like campaignrefinery.com) and your computer queries the DNS system to find the corresponding IP address. 

The server checks various DNS databases to find the IP and returns it to your device, enabling it to connect to the desired website or service. This is how your computer knows where to find the websites you visit.

Reverse DNS Lookup Explained

A DNS reverse lookup is similar to a regular DNS lookup, but in reverse — it takes an IP address and tries to find the domain name associated with it. 

A reverse lookup consists of these 7 steps:

  1. The process begins when a receiving mail server seeks to identify the domain name associated with a given IP address.
  2. The mail server sends a DNS query, formatted specifically for reverse lookup, to a DNS resolver
  3. The DNS resolver starts from the top-level domain (TLD) root servers and iteratively narrows down to the authoritative DNS servers responsible for the IP address range in question.
  4. Upon reaching the appropriate DNS servers, the resolver queries for the PTR records associated with the specified IP address. PTR records, if you recall, are designed to map IP addresses to domain names.
  5. The DNS server, if configured correctly, returns the domain name associated with the provided IP address (which is within the PTR record) back to the mail server.
  6. The mail server then processes the received domain name, using it for various purposes such as authentication, logging, or routing decisions.
  7. If no PTR record is found or the lookup fails for any reason, the DNS server returns an appropriate error response, indicating the absence of a reverse mapping for the given IP address.

This system, which uses DNS records, is highly efficient and has been largely effective so far in making email secure.

When to Use Reverse DNS Lookups

DNS Reverse lookups aren’t just for mail servers — you can use them for other purposes, too. 

If you see an unfamiliar IP address in your server logs, you can do a reverse lookup to see if it gives you any clues about where the traffic is coming from. Or, if you’re suspicious about an email you’ve received, you can run a reverse lookup on the IP address of the sender to see if it matches the domain name they used in the email address.

Note that DNS reverse lookups aren’t always successful. There’s no guarantee every IP address will have a corresponding domain name associated with it. But they can be a useful tool for gathering more information about where internet traffic is coming from.

You could even use reverse lookups for your sales efforts:

  • Reverse DNS lookups can help you track who visits your website. 
  • Beyond just identifying visitors, reverse DNS provides additional info like the country and city associated with an IP address.

Let’s check out how understanding DNS reverse lookups can help your email marketing efforts.

Reverse DNS Lookup: Why Should Email Marketers Care?

You’re probably thinking, hey, all of this sounds really technical; why should I care, as an email marketer?

You should care because reverse DNS lookup plays a crucial role in email marketing, particularly in the aspect of email deliverability and sender reputation. It could also give you information on leads visiting your website.

The biggest benefit of having your reverse DNS records in place are:

  1. Security protocols like SPF and DKIM need them.
  2. ISPs use them.
  3. Google and Yahoo expect you to have them.

For the smooth functioning of your email operations, you must understand each of the three points in detail.

SPF, DKIM, DMARC and Reverse DNS

DNS reverse lookups aren’t just for the normal functioning of emails; they also play a critical role in email authentication. Two critical email security protocols — SPF and DKIM — use reverse DNS lookups to fight malicious email senders.

SPF, DKIM, and DMARC (Domain-based Message Authentication, Reporting & Conformance) are the three main players in the world of email authentication, working together to ensure emails are coming from who they say they are. As DMARC doesn’t deal with reverse lookups, we will only discuss SPF and DKIM.

SPF (Sender Policy Framework)

SPF or Sender Policy Framework checks the IP address of the email server trying to send an email on behalf of your domain (like your company’s email address). 

The SPF record published in your domain’s DNS settings acts as a whitelist, specifying authorized servers allowed to send emails for you. If the email server’s IP isn’t on the list, the SPF check fails, raising a red flag.

DKIM (DomainKeys Identified Mail)

DKIM or DomainKeys Identified Mail acts as a digital signature on the email itself. 

It adds a special code in the email header that only your email server can create using a cryptographic key pair. When the receiving server checks the DKIM signature and verifies it matches the public key published in your domain’s DNS, it confirms the email content hasn’t been tampered with during delivery.

When Does SPF Use Reverse DNS Lookup?

SPF allows domain owners to specify which IP addresses are authorized to send emails on behalf of their domain. When an email server receives a message, it may perform a reverse DNS lookup on the IP address from which the email originated. 

This DNS reverse lookup checks if the domain name obtained from the reverse DNS query matches the domain name specified in the sender’s email address. While SPF itself does not mandate reverse lookups, some receiving email servers may perform them as part of their SPF validation process to enhance authentication.

How about DKIM? 

When a recipient’s email server receives a DKIM-signed message, it can use the sender’s public key retrieved from DNS to verify the DKIM signature. 

While DKIM itself doesn’t directly involve reverse DNS lookups, the process of retrieving the public key from DNS may involve DNS queries. These could include reverse lookups if the public key is stored under a domain name derived from the sending IP address.

Both SPF and DKIM require a proper reverse DNS setup:

ProtocolThe role of reverse DNS
SPFIf an IP address lacks proper DNS setup (including reverse DNS), it might be flagged as spam.
DKIMThe DKIM record’s public key is retrieved via DNS, so a well-configured DNS (including reverse DNS) ensures successful verification.
How SPF and DKIM use reverse DNS records

While SPF and DKIM themselves don’t directly perform reverse DNS lookups, they heavily rely on DNS infrastructure, including reverse DNS records.

Mailbox Providers (ISPs) Use Reverse DNS Lookup, Too

Email servers often maintain lists of known spam sources and use various metrics to assess the reputation of incoming emails. A DNS reverse lookup is one such metric.

Mailbox providers like Gmail or Yahoo use reverse DNS lookups to verify the legitimacy of incoming emails.

And they use both types of DNS lookups:

DNS Lookup TypeHow it works
Forward DNS lookupChecking if the IP address the email originates from has a corresponding email domain name.
Reverse DNS lookupChecking if the domain name matches the sender’s domain name in the email address.
How mailbox providers use DNS lookups 

This helps email servers identify and filter out spam. If your emails lack a proper reverse DNS record, they might be flagged as spam and end up in recipient inboxes or even bounce altogether. This can significantly impact the reach of your email marketing campaigns.

Overall, email servers use reverse DNS lookups as part of their spam filtering, authentication, and reputation assessment processes to help ensure the authenticity of emails.

The 2024 Spam Update from Google and Yahoo Requires DNS Records

For email marketers, ensuring their emails land in inboxes, not spam folders, is crucial. This is why implementing SPF, DKIM, and DMARC authentication protocols is highly recommended, as it has a direct effect on your deliverability. And as of February 2024, both Yahoo and Gmail require bulk email senders to have authentication in place.

The Google and Yahoo 2024 Spam Update: A Game Changer

This spam update raises the bar for email security. By requiring stricter authentication for bulk senders, Google and Yahoo aim to significantly reduce spam and enhance user experience. 

The spam update states:

  1. You must include a clear and functional one-click unsubscribe mechanism.
  2. SPF and DKIM MUST be implemented.
  3. Maintaining a good sender reputation is critical.

For email marketers, this update underscores the importance of SPF, DKIM, and DMARC. Implementing these protocols is no longer optional; it’s essential for you to maintain a good sender reputation and to ensure your emails reach their intended audience.

Cleaning up your DNS records is great for you because:

  • You get improved email deliverability,
  • You’ll be in the good books of regulatory authorities, 
  • Your subscribers won’t experience phishing and spoofing attacks,
  • You get an enhanced brand reputation,
  • DMARC reports allow you to identify unauthorized email activity.

Deliverability is the Goal

Being technically knowledgeable is critical for email marketers if they want to succeed. Especially when it comes to email deliverability, it’s vital you stay in tune with not only new trends in email marketing, but also security updates.

This is where our guidebook — The Inbox Formula — can be an excellent companion. 

This guide explains the details of setting up and running an email operation the right way, so you can achieve the best sender reputation possible. It spells out the specifics of contact management and gives you IP and domain tips/tricks to help you achieve rockstar-level engagement rates.

And there’s no charge; the Inbox Formula is 100% FREE. Download it right now to transform your email marketing chops — we promise you’ll never sleep on these best practices again!

Download The Inbox Formula here.

Campaign Refinery and Email Security: Hand-in-Hand

At Campaign Refinery, we wholeheartedly support all efforts to make email spam-free; we will implement all security measures to help this vision come true. After all, it’s critical that email users feel 100% satisfied with this medium of communication so that we can continue to send marketing emails of value to them.

And this is why:

  • Campaign Refinery requires that all clients implement SPF, DKIM, and DMARC on their domains before they send their first email.
  • We have an application process to ensure only genuine email professionals use our platform to run campaigns.
  • Our platform features an automated list-cleaning tool that detects and neutralizes all invalid emails, which gives a massive boost to your engagement rates plus ensures you avoid spam traps and blacklists.
  • We offer Smart Goal Triggers to help you execute precise campaigns with ease and avoid email fatigue among subscribers.

Also, we closely monitor client activities to ensure:

  1. Open rates don’t drop below 10%,
  2. Bounce rates don’t exceed 10%,
  3. Spam complaint rates don’t go over 0.1%.

In short, you’ll be a part of an exclusive club of email veterans who see elite email performance every day.

If this is the circle you want to enter, apply to be a Campaign Refinery customer today.

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