What is the impact of updating reverse DNS on an MTA and what are the best practices?
Michael Ko
Co-founder & CEO, Suped
Published 26 Apr 2025
Updated 16 Aug 2025
8 min read
Updating the reverse DNS (rDNS) on a Mail Transfer Agent (MTA) is a critical task that directly influences email deliverability. rDNS, also known as a PTR record, provides a crucial layer of authentication by allowing recipient mail servers to verify that an IP address is legitimately associated with a specific hostname or domain. Essentially, it performs the reverse of a standard DNS lookup, mapping an IP address back to its corresponding domain name. This verification process is a key factor in how mail servers decide whether to accept an incoming email or flag it as suspicious. Therefore, when we consider modifying this setting, understanding the potential impacts and adhering to best practices is essential to avoid disruptions in email flow and maintain a strong sender reputation.
The primary goal of rDNS is to combat spam and phishing. Many receiving mail servers perform an rDNS lookup on the connecting IP address as part of their anti-spam checks. If the IP's rDNS record does not match its forward DNS record, or if there is no rDNS record at all, the email might be treated with suspicion. This often results in the message being sent to the spam folder, quarantined, or even outright rejected. Maintaining a proper rDNS configuration is a fundamental aspect of establishing trust with recipient servers and ensuring your legitimate emails reach the inbox.
Even though it might seem like a minor update, changes to an MTA's rDNS record can have cascading effects on email deliverability if not handled meticulously. We’ve seen firsthand how an improperly configured rDNS can lead to emails landing in spam folders, even for reputable senders. This is why thorough planning and immediate validation are non-negotiable.
The role of reverse DNS in email deliverability
The role of reverse DNS in email deliverability
Reverse DNS is a crucial component of email authentication and plays a significant role in how recipient mail servers determine the legitimacy of an incoming email. When your MTA connects to a receiving server, that server often performs a PTR record lookup. This check verifies that the IP address from which the email originated maps back to the hostname specified in the rDNS record. This process is a fundamental anti-spam measure, helping to distinguish legitimate senders from potential spammers or malicious actors who might be using compromised IP addresses.
More specifically, many mail servers require what is known as Forward-Confirmed Reverse DNS (FCrDNS). This means that not only must the IP address have a PTR record that resolves to a hostname, but that hostname must also have a forward (A) record that resolves back to the original IP address. This two-way validation provides a much stronger assurance of authenticity. Without proper FCrDNS, your emails are much more likely to be flagged as spam, regardless of your content or sender reputation.
Sender reputation is built on multiple factors, and rDNS is a foundational one. If your rDNS is misconfigured or missing, it sends a red flag to email providers, negatively impacting your sender reputation. This can lead to increased bounce rates and lower inbox placement, even for mailers with otherwise good practices. Understanding why reverse DNS is important for email sending is crucial for effective deliverability.
Potential impacts of updating reverse DNS on an MTA
Potential impacts of updating reverse DNS on an MTA
When you update the rDNS record for an MTA, the primary impact revolves around how receiving mail servers perceive your sending identity. If the update is performed correctly and all associated records (like the HELO/EHLO banner) are aligned, the impact should be minimal, or even positive, as it solidifies your legitimate sender status. However, if there are inconsistencies or errors in the update, the consequences can be immediate and severe for your email deliverability.
Major mail providers, like Google and Yahoo, extensively use rDNS lookups in their anti-spam algorithms. A mismatch between the connecting IP's PTR record and the hostname presented in the HELO/EHLO banner can be a significant negative signal. This discrepancy might cause your emails to be quarantined, bounced, or subjected to stricter filtering, leading to a noticeable drop in inbox placement. We emphasize how important it is for rDNS to match the SMTP banner.
Proper rDNS update
Positive impact: Reinforces sender authenticity and trust with recipient servers.
Improved deliverability: Less likely to be flagged by spam filters, leading to better inbox placement.
Enhanced reputation: Contributes positively to your overall sending reputation over time.
Reduced bounces: Prevents rejections due to rDNS mismatches.
Improper rDNS update
Deliverability issues: Emails may land in spam, be quarantined, or bounced.
Negative reputation: Can damage your sender reputation, making future sending harder.
Diagnostic complexity: Troubleshooting deliverability problems becomes more complex.
The propagation time for rDNS updates can vary, depending on the TTL (Time To Live) settings of the DNS records involved and local caching. While some changes might propagate quickly, others could take several hours or even a full day. During this transition period, it is possible to experience temporary deliverability fluctuations. This temporary instability is why it is crucial to plan your update during off-peak hours and closely monitor your email performance immediately afterward.
Propagation Considerations for rDNS
While an rDNS update's direct impact is generally minimal if done correctly, the key is the propagation time. This period can introduce temporary mismatches, potentially leading to deliverability issues until the changes fully disseminate across DNS servers worldwide. It's similar to how long reverse DNS takes to propagate.
Always account for this propagation delay and schedule your updates during periods of low email volume to minimize any potential service interruptions or temporary dips in inbox placement rates.
Best practices for updating reverse DNS
Best practices for updating reverse DNS
To ensure a smooth transition and maintain optimal email deliverability, we follow several key best practices when updating an MTA's reverse DNS. The first step is meticulous preparation. Before initiating any changes, ensure that the new hostname you intend to use for your rDNS record is valid, resolves correctly via forward DNS (A record), and is actively used by your MTA in its HELO/EHLO banner. This alignment is critical, as many receiving servers will cross-reference these values. We've seen situations where a mismatch between the rDNS and the HELO/EHLO can cause significant deliverability issues.
The actual update of the PTR record (rDNS) is typically handled by your Internet Service Provider (ISP) or the entity that controls the IP address block. Coordinate with them closely to ensure the correct hostname is assigned to your IP. Once the update is complete, immediately verify the change using an rDNS lookup tool. You can use a command-line tool like nslookup or dig to confirm the new record has propagated:
Verifying rDNS using digBASH
dig -x your.ip.address
Finally, continuous monitoring is non-negotiable. After the update, closely monitor your email delivery rates, bounce logs, and DMARC reports for any anomalies. Pay particular attention to feedback loops from major mailbox providers. If you notice a sudden increase in bounces or a decrease in inbox placement, investigate your rDNS configuration first. We recommend checking relevant blocklists (or blacklists) regularly, as a misconfigured rDNS can lead to an IP being listed automatically by some providers. Maintaining a robust blocklist monitoring strategy is an excellent way to catch and resolve these issues quickly.
Views from the trenches
Views from the trenches
Best practices
Ensure the rDNS hostname precisely matches the HELO/EHLO hostname your MTA uses during SMTP handshake.
Verify that the forward DNS (A record) for your rDNS hostname resolves back to the same IP address for FCrDNS validation.
Confirm there is only one PTR record for your IP address, as some dashboards may create multiple entries leading to issues.
Conduct thorough checks immediately after the rDNS update to confirm propagation and correct resolution.
Common pitfalls
Mismatched rDNS and HELO/EHLO hostnames can lead to immediate deliverability problems and reduced sender trust.
Automated listing on real-time blocklists (RBLs) if rDNS updates are performed incorrectly or inconsistently.
Using a new domain or a generic top-level domain (gTLD) for rDNS might trigger reputation issues with some mailbox providers due to lack of age.
Assuming rDNS propagation is instantaneous; it can take time and may cause temporary disruptions.
Expert tips
Consider the age and TLD of the domain chosen for the rDNS record, as newer or less common gTLDs can sometimes negatively impact initial reputation.
Ensure all other domain authentication records, like SPF and DKIM, are correctly configured and aligned with the new rDNS setup before making changes.
Plan rDNS updates during periods of low email volume to minimize the impact of any unexpected deliverability issues during propagation.
Utilize tools for rDNS lookups and blacklist monitoring to quickly detect and address any problems post-update.
Expert view
Expert from Email Geeks says that if the rDNS does not match the EHLO hostname or SPF entry, it will cause deliverability issues and reputation may be assigned based on the hostname.
2021-11-11 - Email Geeks
Marketer view
Marketer from Email Geeks says that updating the domain on an MTA's reverse DNS shouldn't really cause any issues, but it's important to do it properly the first time to avoid automated listings on prominent RBLs.
2021-11-11 - Email Geeks
Ensuring smooth email flow
Ensuring smooth email flow
Updating reverse DNS on an MTA is a technical task with significant implications for email deliverability. While the change itself can be straightforward, the potential for negative impacts arises primarily from misconfigurations or a lack of alignment across your email infrastructure. A properly updated and aligned rDNS record is a fundamental building block for strong sender reputation and ensures your emails are recognized as legitimate by receiving mail servers.
By adhering to best practices—including careful planning, ensuring consistency with your HELO/EHLO banner, verifying FCrDNS, and diligent monitoring—you can navigate this process seamlessly. Prioritizing these technical aspects is crucial for maintaining inbox placement and avoiding costly deliverability issues caused by blocklists (or blacklists) or stricter spam filtering. Ultimately, a well-configured rDNS contributes to the overall health and effectiveness of your email program.
Google and 
Yahoo, extensively use rDNS lookups in their anti-spam algorithms. A mismatch between the connecting IP's PTR record and the hostname presented in the HELO/EHLO banner can be a significant negative signal. This discrepancy might cause your emails to be quarantined, bounced, or subjected to stricter filtering, leading to a noticeable drop in inbox placement. We emphasize how important it is for rDNS to match the SMTP banner.
