What is reverse DNS (rDNS) and FCrDNS, and how do they impact email sending?
Michael Ko
Co-founder & CEO, Suped
Published 9 Jul 2025
Updated 17 Aug 2025
10 min read
Email deliverability relies on many factors, and two critical components are Reverse DNS (rDNS) and Forward-Confirmed reverse DNS (FCrDNS). While the Domain Name System (DNS) typically translates human-readable domain names into machine-readable IP addresses, rDNS performs the opposite function. It resolves an IP address back to its associated domain name. This 'reverse' lookup is a fundamental security and authentication check in the email ecosystem, influencing whether your emails land in the inbox or are flagged as suspicious.
Understanding how rDNS and FCrDNS work, and their impact on your email sending, is vital for maintaining a strong sender reputation and ensuring high deliverability rates. Many mail servers and anti-spam systems perform these checks to verify the legitimacy of incoming email, making them crucial for anyone involved in email marketing, transactional emails, or general email communication. If your rDNS is not correctly configured, your legitimate emails could easily be caught by spam filters or even rejected outright by recipient servers. We'll explore why these records are so important and how they fit into the broader landscape of email security.
Essentially, these DNS lookups act as a trust mechanism. When an email server receives an email, it often wants to confirm that the sender's IP address is genuinely associated with the domain it claims to be sending from. This helps prevent spoofing and phishing attempts. Neglecting rDNS and FCrDNS can significantly impact your email's journey to the inbox, making it harder to build and maintain a positive sender reputation.
What is reverse DNS (rDNS)?
Reverse DNS (rDNS) is the process of resolving an IP address back to a domain name, essentially the opposite of a standard DNS lookup. While a typical DNS query (an A record lookup) translates domain.com to an IP address, an rDNS query takes an IP address and returns the associated domain name. This reverse mapping is stored in a Pointer Record, or PTR record, within the DNS.
For email sending, rDNS plays a critical role in verification and anti-spam efforts. When an email server receives an incoming connection, it often performs an rDNS lookup on the connecting IP address. This allows the receiving server to verify that the IP address matches the domain name provided in the HELO or EHLO command during the SMTP handshake. If there's no PTR record or if it points to a generic or unexpected domain, it can raise a red flag, potentially leading to your email being sent to spam or rejected. This is why rDNS is important for email sending.
Example PTR record for IPv4dns
81.233.202.162.in-addr.arpa. IN PTR mta1.yourdomain.com.
A properly configured PTR record signals that the sending server is legitimate and that its IP address is correctly associated with a specific hostname. This adds a layer of trust, making it less likely for your emails to be viewed as spam. In many cases, it is a basic requirement for your emails to be accepted by certain mail servers at all. Therefore, ensuring your rDNS is set up correctly is a fundamental step toward achieving good email deliverability and avoiding email blacklists or blocklists.
The significance of FCrDNS for email deliverability
While rDNS checks for a reverse mapping, Forward-Confirmed reverse DNS (FCrDNS) takes this verification a step further. FCrDNS ensures that both the rDNS lookup and a subsequent forward DNS lookup (A record) resolve correctly and match each other. In other words, an FCrDNS check involves two steps:
Reverse lookup: The receiving mail server performs an rDNS lookup on the connecting IP address to retrieve its associated hostname.
Forward lookup confirmation: It then performs a regular forward DNS lookup on the hostname obtained from the rDNS query. The IP address returned by this forward lookup must match the original connecting IP address.
This two-step process provides a strong level of assurance that the sender's IP address and hostname are authentically linked and not being spoofed. Many major Internet Service Providers (ISPs) and email providers, like Google and Yahoo, consider FCrDNS a critical factor in their spam filtering algorithms and compliance requirements. A failure in FCrDNS is often a strong indicator of a potential spam source or a misconfigured server. Learn more about FCrDNS from Word to the Wise.
Why FCrDNS matters
FCrDNS is a strong signal of legitimacy. It assures the receiving server that the sending IP address is not only associated with a domain but that the domain also legitimately points back to that IP. This consistency builds trust and helps prevent your emails from being flagged.
Consequences of FCrDNS failure
If an FCrDNS check fails, email servers are highly likely to treat your messages with suspicion, often leading to rejection or immediate placement into the spam folder. This directly impacts your domain reputation.
For email service providers (ESPs) and organizations managing their own mail servers, proper FCrDNS setup is a non-negotiable best practice. It’s a core component of verifying sender identity, alongside other authentication mechanisms like SPF, DKIM, and DMARC. Without it, even perfectly crafted emails with valuable content might not reach their intended recipients, drastically affecting your overall email campaign performance.
Impact on email deliverability and sender reputation
The impact of rDNS and FCrDNS on email deliverability cannot be overstated. When a mail server receives an email, one of the first things it does is a series of checks to determine the sender's legitimacy. This includes verifying the IP address from which the email originated. A correctly configured rDNS (and especially FCrDNS) record tells the receiving server that the sending IP is legitimate and associated with a real, verifiable domain. This acts as a trust signal, helping your emails bypass spam filters and reach the inbox.
Conversely, a missing, generic, or mismatched rDNS record immediately raises suspicion. Many receiving mail servers are configured to reject emails from IP addresses that fail these checks or send them directly to the spam or junk folder. Spammers often use IP addresses with generic or no PTR records, making this a common criterion for blocklists (or blacklists). If your rDNS is missing or different, your deliverability will suffer.
Properly configured rDNS/FCrDNS
Trust and reputation: Builds confidence with receiving mail servers, indicating a legitimate sender and positively impacting your domain reputation.
Inbox placement: Significantly increases the likelihood of emails landing in the primary inbox rather than spam.
Compliance: Meets a common requirement for many large email providers like Outlook.
Missing or misconfigured rDNS/FCrDNS
Spam categorization: Emails are often automatically classified as spam or junk.
Email rejection: Servers may reject emails entirely, leading to bounces and non-delivery.
Reputation damage: A poor rDNS setup can negatively affect your sender score and increase the likelihood of being listed on a blocklist or blacklist.
It’s not just about avoiding spam filters, but also about establishing your domain's credibility. Sender reputation is a cumulative score based on various factors, and rDNS is a foundational element. A proper setup signals to mail servers that you are a legitimate sender following best practices, which is crucial for building and maintaining a positive sender score over time. Without proper rDNS and FCrDNS, even the best email content and list hygiene practices may not be enough to overcome the initial hurdle of server-side validation.
Managing rDNS for email sending
Who is responsible for managing rDNS often depends on how you send emails. If you use a third-party Email Service Provider (ESP) to send your emails, they typically manage the rDNS records for the IP addresses they use. This is common because ESPs control the IP addresses from which your emails are sent. You generally won't need to configure rDNS yourself when using an ESP, although it's always good practice to verify their configuration, especially if you encounter deliverability issues.
However, if you operate your own mail server (MTA) or use a cloud provider where you manage your own IP addresses, then you are responsible for setting up and maintaining the rDNS records. This typically involves contacting your Internet Service Provider (ISP) or cloud hosting provider to request the creation or modification of PTR records for your sending IPs. This is a crucial step for any organization managing its own email infrastructure, particularly when configuring rDNS for dedicated IP addresses.
For organizations using email services like Amazon SES or Google Workspace (Gmail for business), rDNS is typically managed by the provider for their shared IP pools. If you opt for dedicated IPs with such services, they will provide instructions on how to set up or request the rDNS configuration. In cases where your company email is hosted by a service like Gmail, but you're receiving reports about rDNS issues, it might indicate that email is being sent from an IP not intended for mail sending or from a misconfigured third-party application. It's essential to investigate your email headers to determine the actual sending IP.
Regardless of whether you manage your own server or use an ESP, ensuring that your rDNS (and FCrDNS) is correctly configured and matches your outgoing HELO/EHLO hostname is a fundamental step towards maximizing your email deliverability and maintaining a healthy sender reputation. You can also monitor your blocklist monitoring to proactively identify any issues.
Views from the trenches
Best practices
Always ensure your sending IPs have a valid PTR record that resolves to a hostname that also resolves back to the same IP (FCrDNS).
If using an ESP, confirm they handle rDNS appropriately, especially if you have a dedicated IP. It is usually their responsibility.
Regularly check your email headers to confirm the sending IP and its corresponding rDNS record, especially if using a new email service or server.
For self-hosted MTAs, configure a dedicated IP address with a specific, non-generic hostname for your mail server and set up the PTR record.
Align your HELO/EHLO hostname with your FCrDNS entry to prevent mismatches that can trigger spam filters.
Common pitfalls
Sending emails from IP addresses with generic or missing rDNS records, often from consumer IP pools or misconfigured cloud nodes.
Assuming an ESP automatically configures FCrDNS for all sending scenarios, particularly when using your own IPs.
Not understanding that a 'generic' reverse DNS is a sign of a server not intended for mail, leading to poor deliverability.
Failing to confirm the sending IP in email headers, leading to misdiagnosis of rDNS issues or overlooking problematic sending sources.
Ignoring rDNS warnings from monitoring tools, leading to decreased deliverability and a damaged sender reputation.
Expert tips
If you're operating an MTA and aren't familiar with FCrDNS, consider if self-hosting is the right path.
For ESPs, unless you're bringing your own IPs, rDNS should not typically be a concern, as the provider usually handles it.
When a mail server connects to a recipient server, the HELO/EHLO hostname should match the PTR record for the connecting IP.
Generic reverse DNS indicates an IP from a consumer pool or an unconfigured server, making mail delivery difficult.
Regularly review your email sending practices and infrastructure to ensure rDNS and FCrDNS compliance.
Marketer view
Marketer from Email Geeks says that their provider (email or CRM) should manage the PTR record and that sending MTAs need FCrDNS.
2024-01-22 - Email Geeks
Marketer view
Marketer from Email Geeks explains that a PTR record is the reverse of an A record, so an IP like 10.1.1.2 would have a PTR record pointing back to mta1.yourdomain.com if the A record for mta1.yourdomain.com points to 10.1.1.2.
2024-01-22 - Email Geeks
Ensuring optimal email delivery
In summary, Reverse DNS (rDNS) and Forward-Confirmed reverse DNS (FCrDNS) are fundamental pillars of email deliverability and security. They act as essential verification mechanisms, allowing receiving mail servers to confirm the legitimate association between a sending IP address and its declared domain. Proper configuration of PTR records and ensuring FCrDNS compliance are not mere technicalities, but critical steps to ensure your emails reach their intended recipients. These checks help prevent spoofing and contribute significantly to your overall sender reputation and inbox placement.
Whether you rely on an Email Service Provider or manage your own mail server, understanding and actively managing these DNS records is paramount. Neglecting them can lead to your emails being flagged as spam or rejected outright, undermining your communication efforts and potentially damaging your brand's credibility. By adhering to best practices for rDNS and FCrDNS, you strengthen your email authentication, build trust with recipient servers, and significantly improve your chances of achieving consistent email deliverability.
Staying proactive with your email infrastructure, including DNS configuration, is key to navigating the complex landscape of email security and ensuring your messages arrive where they belong: in the inbox. For more insights into common deliverability challenges and solutions, explore our guide on why your emails fail.
Google and 
Yahoo, consider FCrDNS a critical factor in their spam filtering algorithms and compliance requirements. A failure in FCrDNS is often a strong indicator of a potential spam source or a misconfigured server. Learn more about FCrDNS from Word to the Wise.
Outlook.
Amazon SES or 
Google Workspace (Gmail for business), rDNS is typically managed by the provider for their shared IP pools. If you opt for dedicated IPs with such services, they will provide instructions on how to set up or request the rDNS configuration. In cases where your company email is hosted by a service like Gmail, but you're receiving reports about rDNS issues, it might indicate that email is being sent from an IP not intended for mail sending or from a misconfigured third-party application. It's essential to investigate your email headers to determine the actual sending IP.
