How do I perform a reverse DNS lookup and interpret the results?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 Jun 2025
Updated 19 Aug 2025
8 min read
When you send an email, your mail server acts like a digital post office. Just as a physical post office has an address, your mail server has an IP address. For email recipients to trust that your mail is legitimate and not spam, they often perform a quick check, essentially asking, "Who is sending this mail?" This question is answered by a reverse DNS (rDNS) lookup.
Reverse DNS is a crucial component of email deliverability. Without it, your emails are more likely to be flagged as suspicious and land in the spam folder, or even be rejected outright. Understanding how to perform an rDNS lookup and interpret its results is essential for maintaining a healthy sending reputation and ensuring your messages reach the inbox.
In this article, I will walk you through the process of performing a reverse DNS lookup and explain what the results mean for your email sending. Whether you're a seasoned email marketer or a system administrator, mastering rDNS checks is a fundamental step in ensuring optimal email performance.
What is reverse DNS (rDNS)?
At its core, reverse DNS (rDNS) is the opposite of a standard DNS lookup. A regular DNS lookup translates a domain name (like example.com) into an IP address (like 192.0.2.1). Reverse DNS, on the other hand, takes an IP address and resolves it back to a domain name. This translation is managed by a specific type of DNS record called a Pointer (PTR) record.
For email, the rDNS record typically points to the hostname of the sending mail server. When a receiving email server gets a message, it performs an rDNS lookup on the sending IP address. It then checks if the hostname returned by this lookup matches the hostname advertised by the sending server in its HELO/EHLO command. This process, known as a full circle reverse DNS check (FCrDNS), adds a layer of authenticity to the email origin.Learn more about FCrDNS checks.
PTR records are essential for establishing trust in the email ecosystem. They help confirm that the sender is who they claim to be and that the IP address isn't being used by spammers. Without a correctly configured PTR record, your emails might be viewed with suspicion, regardless of your other authentication measures like SPF or DKIM.
Why reverse DNS matters for email deliverability
Reverse DNS plays a critical role in email deliverability, primarily because it's a key factor in how email providers and anti-spam systems assess sender reputation. Many Mail Transfer Agents (MTAs) and spam filters use rDNS to verify the legitimacy of incoming connections. If an IP address lacks a valid rDNS record, or if the rDNS record doesn't align with the sending domain, it raises a red flag.
Spammers often send emails from IP addresses that either have no rDNS configured or have generic, non-descriptive rDNS entries. By requiring a proper rDNS setup, receiving servers can filter out a significant portion of unsolicited mail. This is why a missing or misconfigured rDNS can lead to your emails being rejected or sent directly to the spam or junk folder, even if your content is legitimate.Discover more about rDNS and spam filters.
Furthermore, many email blocklists (or blacklists) include IP addresses without valid rDNS entries. Getting listed on such a blacklist can severely impact your ability to deliver emails. Therefore, ensuring your IP has a correct reverse DNS record is a foundational step in building and maintaining a good sender reputation and avoiding common deliverability pitfalls.Understand how email blocklists function.
How to perform a reverse DNS lookup
Performing a reverse DNS lookup is straightforward, whether you prefer command-line tools or web-based utilities. Both methods query DNS servers for the PTR record associated with an IP address, providing similar results but with different levels of detail.
Command line tools
On Windows, the nslookup command is commonly used. Open your Command Prompt and type:
Windows nslookup commandbash
nslookup [IP_ADDRESS]
For Linux or macOS, dig (Domain Information Groper) is the preferred tool, offering more detailed DNS query results. Open your Terminal and type:
Linux/macOS dig commandbash
dig -x [IP_ADDRESS]
Online tools
Several online tools also provide reverse DNS lookup capabilities, often with a user-friendly interface. These are great for quick checks without needing to access a command line. A reliable option is DNSChecker.org's reverse DNS tool. Simply enter the IP address and initiate the search.
These tools will query DNS servers and return the associated PTR record, or indicate if no record exists. The output may vary slightly between tools, but the core information, the resolved hostname, will be present if a record is found.
Interpreting the results
Once you perform an rDNS lookup, understanding the output is key. A successful lookup will return a domain name, indicating that a PTR record exists for the IP address. The ideal scenario for email deliverability is when the reverse DNS entry (PTR record) matches the forward DNS entry (A record) of your sending domain. This is known as a Full Circle Reverse DNS (FCrDNS) match.Verify your IP and PTR record.
For example, if your sending IP is 192.0.2.1 and its PTR record resolves to mail.example.com, a successful FCrDNS check would mean that mail.example.com also resolves back to 192.0.2.1 via its A record. This consistency provides strong proof of legitimacy to receiving mail servers, significantly boosting your email's chances of reaching the inbox.
Conversely, if the lookup returns no record, a generic hostname, or a hostname that doesn't correspond to your sending domain, it indicates a problem. Receiving mail servers may view this as a sign of potential spam or malicious activity and are likely to either reject your email or classify it as spam.Find more details on reverse DNS.
Understanding good versus bad rDNS
Good rDNS configuration
PTR record exists: The IP address resolves to a specific, legitimate hostname (e.g., mail.yourdomain.com).
FCrDNS match: The hostname in the PTR record resolves back to the same IP address via its A record, ensuring consistency.
Descriptive hostname: The hostname clearly indicates it's a mail server for your domain.
Impact on deliverability
A good rDNS configuration builds trust with receiving mail servers. It signals that your email server is properly configured and not a source of spam. This significantly improves your sender reputation and ensures higher inbox placement rates for your emails.
Incorrect rDNS configuration
No PTR record: The lookup returns no associated domain name.
Mismatched FCrDNS: The PTR record points to a hostname that doesn't resolve back to the original IP, or to a different domain.
Generic hostname: The hostname is a generic server name provided by a hosting provider (e.g., ip-192-0-2-1.static.host.com).
Impact on deliverability
Poor or missing rDNS significantly harms your sender reputation. Emails might be rejected with errors like "Reverse DNS lookup failed" or simply routed to spam. This can lead to significant deliverability issues and bounce rates.
I’ve encountered many situations where perfectly legitimate emails were blocked because of an rDNS mismatch. It's a fundamental check that many email providers perform. Ensuring your rDNS is properly configured and matches your sending domain is not just a best practice, but a necessity for reliable email delivery.
Troubleshooting common rDNS issues
If your reverse DNS lookup reveals an issue, such as a missing PTR record or a mismatch, it's crucial to address it promptly. The process for fixing rDNS usually involves contacting your Internet Service Provider (ISP) or hosting provider, as they typically control the PTR records for your assigned IP addresses.
When you contact them, you will need to provide the IP address(es) you are sending from and the desired hostname you want the PTR record to point to (e.g., mail.yourdomain.com). It's vital that this hostname is a valid, existing domain that you control and that it has an A record pointing back to the same IP address.Understand the impact of updating reverse DNS.
Important steps for fixing rDNS issues
Identify the owner: Determine who manages your IP address block. This is usually your hosting provider or ISP.
Prepare information: Have your sending IP address and the desired hostname ready. Ensure the hostname already has a matching A record.
Submit request: Submit a support ticket or follow their specific procedure for updating PTR records.
Verify after propagation: After a few hours (due to DNS propagation), re-run your rDNS lookup to confirm the change.
Sometimes, issues arise due to complex ISP setups, such as those involving major telecommunications companies. For instance, some providers might route mail through different back-end infrastructures, leading to unexpected rDNS failures. This can be particularly frustrating when you are trying to submit a ticket to an email provider like AT&T or Yahoo to resolve deliverability issues. Knowing your correct IP, rDNS, and associated domain is essential for clear communication with support teams and efficient troubleshooting.Address AT&T reverse DNS failures.
Views from the trenches
Best practices
Always ensure your PTR record points to a fully qualified domain name (FQDN) that resolves back to your IP address.
Regularly check your rDNS configuration, especially after any IP address or server changes, to prevent unexpected deliverability issues.
If using a third-party email service provider, confirm with them how they handle rDNS for your sending IPs, as they often manage it.
Maintain separate, distinct rDNS entries for transactional and marketing emails if you use different IP addresses for each.
Common pitfalls
Forgetting to configure a PTR record for new sending IPs, leading to immediate spam flagging.
Having a generic hostname in your PTR record, which can be interpreted as suspicious by receiving mail servers.
Mismatched forward and reverse DNS records (FCrDNS failure), causing authentication failures and rejections.
Assuming rDNS is automatically handled by your provider without verification, resulting in hidden deliverability problems.
Expert tips
Implement automated monitoring for your rDNS records to detect changes or misconfigurations as soon as they occur.
When dealing with ISPs or telcos for rDNS updates, provide clear, concise information about your IP and desired hostname to expedite the process.
Keep an eye on bounce messages related to rDNS failures, as they provide direct feedback on issues needing attention.
For shared IP addresses, ensure the ESP manages rDNS appropriately to avoid reputation issues from other senders.
Marketer view
Marketer from Email Geeks says they had trouble identifying the ISP for ameritech.net, noting that a customer wasn't receiving specific paid service emails even though send logs indicated acceptance.
2020-10-08 - Email Geeks
Marketer view
Marketer from Email Geeks says that Prodigy seemed to be accepting email for ameritech.net based on their MX record lookups.
2020-10-08 - Email Geeks
Maintaining your email credibility
Reverse DNS is more than just a technical detail; it's a fundamental aspect of establishing trust and credibility for your email sending. A properly configured rDNS, with a matching PTR record, reassures receiving mail servers that your emails are coming from a legitimate source, not a spammer.
By actively monitoring and correcting any rDNS discrepancies, you can significantly reduce the likelihood of your emails being blocked or marked as spam. This proactive approach not only safeguards your sender reputation but also ensures your messages consistently reach their intended recipients, bolstering your overall email deliverability.
AT&T or 
Yahoo to resolve deliverability issues. Knowing your correct IP, rDNS, and associated domain is essential for clear communication with support teams and efficient troubleshooting.Address AT&T reverse DNS failures.
