How does missing or different reverse DNS (rDNS) impact email deliverability, and when is a dedicated IP address needed?
Michael Ko
Co-founder & CEO, Suped
Published 18 Apr 2025
Updated 17 Aug 2025
8 min read
Email deliverability relies on many factors, with sender authentication playing a crucial role. Among these, reverse DNS (rDNS) is a foundational element that helps receiving mail servers verify the identity of the sender. While it might seem like a technical detail, a missing or incorrectly configured rDNS record can significantly impact whether your emails land in the inbox or are flagged as spam.
Understanding rDNS, also known as a Pointer (PTR) record, is essential for any sender, whether you use a shared IP address or have a dedicated one. This record essentially performs the opposite function of a standard DNS A record: instead of translating a domain name into an IP address, it maps an IP address back to a domain name. This reverse lookup is a key step in many anti-spam checks.
The consequences of poor rDNS configuration
A missing or different reverse DNS (rDNS) record can have a direct and often negative impact on your email deliverability. When a receiving mail server gets an email, one of the first things it does is a reverse DNS lookup on the sending IP address. It expects to find a corresponding domain name, and ideally, for that domain name to then resolve back to the original IP address (known as Forward Confirmed Reverse DNS or FCrDNS).
If the rDNS record is missing, generic, or doesn't match the SMTP banner of the sending server, it raises a red flag. Mailbox providers, especially large ones like Google and Yahoo, have tightened their requirements, making proper rDNS a critical component of their anti-spam filtering. Enterprise filters can be even more stringent, often rejecting emails outright from servers with gross misconfigurations.
This doesn't necessarily mean every IP in an ESP's sending range must have a perfectly aligned rDNS if it's not actively sending mail, but any IP actually used for sending must have a correct and valid rDNS record that resolves properly. Without it, your emails are much more likely to be sent to the spam folder or blocked entirely.
The importance of rDNS for email
Trust and legitimacy: rDNS provides a layer of authentication, helping to confirm that the sending server is legitimate and not a spam operation.
Anti-spam filtering: Many anti-spam systems use rDNS as a primary check. A mismatch or absence can trigger higher spam scores.
Recipient server policies: Some email servers are configured to reject mail from IPs without valid rDNS records.
Reverse DNS in a shared IP environment
When using an email service provider (ESP) with shared IP addresses, it's common to find that the rDNS entries across their IP ranges might differ, or some might even lack rDNS values. This isn't inherently problematic for deliverability, provided that the specific IP address used to send your email has a properly configured rDNS record. ESPs often manage large pools of IPs, and not all of them may be active sending IPs with dedicated rDNS. The key is what the rDNS looks like for the IP that actually sends your mail.
ESPs are responsible for setting up and managing the rDNS for their shared IP addresses. Typically, they will configure the rDNS to point to one of their own domains or a generic hostname, not your specific sending domain. This is generally acceptable, as long as it's a valid, publicly resolvable hostname. While ideal rDNS (pointing directly to your domain) can enhance trust, it's not strictly necessary on a shared IP, as long as the record exists and is legitimate.
The greater concern with shared IPs often lies with the sending habits of other users on that same IP. If a shared IP is blocklisted due to another user's spammy behavior, your emails will be affected, regardless of your rDNS setup. Therefore, a robust blocklist monitoring strategy is crucial when relying on shared infrastructure.
Shared IP rDNS
Ownership: Managed by the ESP or hosting provider.
Common configuration: Often points to the ESP's generic domain or a hostname.
Impact on reputation: Less direct control. Reputation is influenced by all senders on the shared IP.
Dedicated IP rDNS
Ownership: Managed by you or your ESP on your behalf.
Common configuration: Typically points to your own sending domain for full alignment.
Impact on reputation: Full control over IP reputation. Your sending practices directly determine performance.
When a dedicated IP is truly necessary
The decision to use a dedicated IP address isn't solely, or even primarily, driven by rDNS configuration. While a dedicated IP allows you to perfectly align your rDNS to your sending domain, the volume of emails you send is no longer the sole determining factor for needing one. A volume of around 40,000 emails per week (or 160,000 per month) is often still well within the scope of a good shared IP pool, especially if the email content is transactional or highly engaged.
A dedicated IP provides you with complete control over your sender reputation. This means your deliverability is not impacted by the sending habits of others. This control becomes more important for senders who:
Send high volumes: Although volume isn't the only factor, very large senders (millions of emails monthly) benefit from the isolation of a dedicated IP.
Have specific sending patterns: For example, highly variable sending volumes or specific types of email, like cold outreach, which can benefit from a more controlled environment.
Require strict brand control: To ensure all aspects of their email infrastructure align with their brand identity, including rDNS.
Experience recurring deliverability issues: If you constantly struggle with inbox placement on shared IPs due to others' poor sending habits, a dedicated IP might be a solution, but it requires diligent warming and monitoring. Learn more about when a dedicated IP can solve issues.
For many, especially those sending moderate volumes, a well-managed shared IP pool with good rDNS configurations and other authentication records (like SPF, DKIM, and DMARC) in place will perform just as well, if not better, than a dedicated IP if it's not warmed properly.
Beyond rDNS: a holistic view of deliverability
Beyond rDNS, a holistic approach to email deliverability is vital. This includes properly configuring all email authentication protocols, maintaining a clean and engaged email list, and consistent sending practices. Mailbox providers look at the full picture of your sending behavior and technical setup. For instance, Microsoft and Google now explicitly require DMARC with a p=none minimum policy. If your emails aren't authenticated properly, they're at a significant disadvantage.
Regularly monitoring your deliverability metrics, including inbox placement rates, spam complaints, and bounce rates, will provide insights into the health of your sending program. Tools like DMARC monitoring and blocklist checkers are essential for proactive management. This comprehensive approach ensures that rDNS is just one piece of a well-optimized deliverability puzzle.
How to check an IP's rDNS (PTR record)BASH
dig -x 192.0.2.1 PTR
Remember, even if your rDNS is perfect, other factors can still lead to deliverability issues. These include poor sender reputation, high spam complaint rates, sending to invalid email addresses (leading to bounces), and lacking proper email authentication.
Views from the trenches
Best practices
Ensure all actively sending IP addresses have a valid, resolvable rDNS record, even on shared IPs.
For dedicated IPs, configure rDNS to point to your primary sending domain for optimal alignment.
Regularly monitor your IP's rDNS configuration to detect any accidental changes or deletions.
Combine proper rDNS with other authentication like SPF, DKIM, and DMARC for a stronger sender profile.
Prioritize maintaining a clean email list and engaging with your subscribers to build reputation.
Common pitfalls
Assuming rDNS is only for dedicated IPs; it's important for shared IPs too.
Ignoring generic or missing rDNS records on IPs actually used for sending.
Switching to a dedicated IP solely for rDNS alignment without addressing other deliverability issues.
Not warming up a new dedicated IP address properly, regardless of rDNS setup.
Focusing only on technical setup and neglecting content quality or audience engagement.
Expert tips
Confirm that your rDNS provides a full forward-confirmed reverse DNS (FCrDNS) setup.
While good, perfect rDNS alignment is less critical now than a strong overall sender reputation.
For moderate volumes, a well-maintained shared IP pool can often outperform a poorly managed dedicated IP.
Evaluate dedicated IP needs based on control over reputation and specific sending patterns, not just volume.
Always verify the rDNS of the specific IP that sends your emails, not just the entire range.
Expert view
Expert from Email Geeks says missing reverse DNS records significantly impact delivery, especially with enterprise filters, as Google and Yahoo require round trip DNS.
2023-12-14 - Email Geeks
Expert view
Expert from Email Geeks says different reverse DNS entries across an IP range are not an issue unless specific problematic patterns are present.
2023-12-14 - Email Geeks
The full picture of rDNS and dedicated IPs
While missing or incorrect reverse DNS can definitely impact your email deliverability, especially with stricter recipient servers, it's just one piece of the puzzle. For senders on shared IPs, the crucial factor is whether the specific IP used for sending has a valid rDNS record, even if it's managed by the ESP.
The need for a dedicated IP address hinges more on factors like control over your sender reputation, specific sending patterns, and volume that truly warrants isolating your sending. For many, a well-managed shared IP environment with robust authentication and good sending practices remains highly effective. Always prioritize a comprehensive approach to email deliverability, continuously monitoring all technical and engagement aspects of your email program.
