Summary
The alignment of reverse DNS (PTR records) with the SMTP banner, specifically the hostname your mail server uses in its HELO/EHLO command, is generally considered a best practice for email deliverability. While a mismatch might not explicitly break email sending, it can signal a lack of proper configuration and potentially reduce trust with receiving mail servers, impacting your sender reputation and inbox placement. Many email servers and spam filters perform these checks to verify legitimacy and prevent spam, making accurate configuration a useful step in demonstrating a professional and legitimate sending posture.
Key findings
- Best practice: Matching reverse DNS to the SMTP banner is a recommended best practice for professional email sending, even if not strictly enforced by all receivers.
- Trust and reputation: Proper alignment contributes to a sender's trustworthiness, which can improve email deliverability and reduce the likelihood of messages being flagged as spam.
- Anti-spam measure: Some spam filters and email servers use this match as a verification step, helping to prevent unauthorized or malicious sending. This is a common check for blocklists (or blacklists).
- Not a hard fail: A mismatch typically does not cause emails to be outright rejected, but it can negatively influence how a receiving server scores your email.
- Verification of legitimacy: The match helps receiving servers confirm that the sending IP address is associated with the domain it claims to be, verifying the sender's identity. To learn more about this, read our article why is reverse DNS important for email sending?
Key considerations
- Technical setup: Ensuring this alignment requires proper configuration of your mail server's hostname and a corresponding PTR record, typically managed by your IP provider or ESP. Our guide on best practices for reverse DNS resolution offers more insights.
- Dedicated IP vs. shared IP: If you have a dedicated IP, you have more control over this. With shared IPs, the ESP manages it, which may be explained in their documentation on reverse DNS white labeling.
- Monitoring: Regularly check your DNS and SMTP banner configuration using online tools to ensure consistent alignment and prevent deliverability issues.
- Impact on deliverability: While not as critical as SPF or DKIM, a misaligned reverse DNS can contribute to a poorer sender reputation, potentially leading to emails landing in spam folders.
What email marketers say
Email marketers often encounter the "Reverse DNS does not match SMTP banner" warning when using deliverability testing tools. While some initially dismiss it, a common consensus among marketers is that it's a simple, cost-free fix that contributes to a more professional sending image and can prevent minor, yet cumulative, deliverability issues. Many seek guidance from their ESPs, like HubSpot, to ensure this alignment, especially when using dedicated IPs.
Key opinions
- Tool flags: Marketers frequently see this issue flagged by email health check tools, prompting them to investigate its importance.
- Simple fix: Many marketers view this as a trivial adjustment, often handled by their ESP, making it an easy win for deliverability.
- Professional image: Aligning these records is seen as a way to project a competent and professional sending presence, which can subtly influence inbox placement.
- Avoiding errors: Some marketers report that failure to align can lead to deliverability errors, even if not a complete block.
Key considerations
- ESP reliance: Marketers often depend on their Email Service Providers (ESPs) to manage the reverse DNS setup, especially for dedicated IP addresses.
- Dedicated IP implications: For those with dedicated IPs, ensuring the PTR record aligns with the SMTP banner is a direct responsibility or collaboration with their ESP. Read more about how rDNS impacts deliverability with dedicated IPs.
- Broader impact: While this specific issue might seem minor, it fits into the larger picture of technical settings that cumulatively affect overall email deliverability issues.
Marketer view
Marketer from Email Geeks explains that they are focusing on understanding the technical aspects of deliverability, using tools like MXToolbox to identify what configurations are important and what are not. They are trying to learn how each aspect contributes to overall email health and performance.
Marketer view
Email marketer from help.gohighlevel.com suggests that properly setting up reverse DNS (rDNS) is a key best practice for email sending. They emphasize that fixing a "Reverse DNS does not match SMTP Banner" issue is a crucial step in improving deliverability.
What the experts say
Email experts largely agree that while a reverse DNS to SMTP banner mismatch won't necessarily cause emails to bounce, it's a strong indicator of a suboptimal mail server setup. It reflects on the sender's professionalism and can subtly influence receiving servers, contributing to a less trusted sending reputation. They emphasize that aligning these records is a straightforward, zero-cost adjustment that is part of looking competent and professional.
Key opinions
- Inbound vs. outbound: Some experts initially suggest this applies more to inbound mail, but quickly clarify its relevance for outbound deliverability, impacting how your sending server is perceived.
- Competence signal: A matching configuration signals that the mail server is properly set up and managed, which can positively influence receiving server trust.
- Not a critical failure point: While not a break in email sending, it’s a factor in the overall assessment of sender legitimacy by receiving mail servers.
- Trivial to align: Experts highlight that achieving this alignment is usually straightforward and incurs no additional cost, making it an easy improvement to implement.
- Impact on HELO/EHLO: The hostname in the SMTP banner (used in HELO/EHLO) should ideally have a matching reverse DNS, establishing a credible round-trip verification. You can learn more about how PTR records and HELOs impact deliverability.
Key considerations
- Sender reputation: While a mismatch doesn't immediately blacklist you, it contributes to a lower sender score, increasing the risk of landing in spam. This can impact your overall IP and domain reputation.
- ISP/ESP involvement: For senders using an ESP with a dedicated IP or managing their own server, direct communication with the provider is key to ensuring PTR records are correctly configured to match the SMTP banner. Read more about this on Spam Resource.
- Diagnostic tools: Utilizing specialized tools to analyze mail server configuration can provide valuable insights into these technical aspects.
Expert view
Expert from Email Geeks clarifies that the issue of reverse DNS not matching the SMTP banner primarily applies to inbound mail, but also notes that a mail server should be properly configured with its hostname. This indicates a general expectation of proper server setup, even if not a critical deliverability factor.
Expert view
An expert from Word to the Wise explains that the primary concern for deliverability relates to the sending server's configuration and its DNS settings. They state that while a mismatch won't break email sending, it is generally good practice for the HELO hostname to align with its DNS hostname (round-trip reverse DNS) to ensure a competent and professional appearance.
What the documentation says
Technical documentation consistently highlights the role of reverse DNS (rDNS) and its alignment with the SMTP banner as a crucial component of email authentication and spam prevention. It defines rDNS as the process of resolving an IP address back to a hostname, which email servers use for legitimacy verification. A mismatch is often flagged as a potential issue, indicating that many receiving systems perform these checks to enhance security and deliverability.
Key findings
- Identity verification: Documentation confirms that this alignment is a key method for email servers and spam filters to verify the sender's identity, ensuring the IP matches the domain it claims to be sending from.
- Spam prevention: It's explicitly stated that checking for this match helps prevent spam by identifying potentially malicious or misconfigured senders. This is particularly relevant for DNSBLs (DNS Blocklists), which often consider such mismatches. Learn more about DNSBLs and deliverability.
- PTR record function: Reverse DNS relies on PTR records, which map an IP address back to a domain name, completing the reverse lookup process.
- Deliverability improvement: Proper rDNS setup, including the banner match, is listed as a fundamental step to improve overall email deliverability rates.
Key considerations
- Technical definition: Reverse DNS is defined as determining a domain name or hostname from an IP address, the opposite of a typical DNS lookup.
- Configuration management: Managing this involves setting up or verifying PTR records, often through the hosting provider or ISP. Understanding missing or different reverse DNS is important.
- White labeling: Using rDNS for white labeling promotes brand recognition and professionalism, suggesting a benefit beyond just avoiding spam filters. Mailgun provides good information on reverse DNS white labeling.
Technical article
Documentation from SMTPBD.COM states that verification of legitimacy is a key reason why many email servers and spam filters check whether the SMTP banner aligns with the reverse DNS entry. This process is crucial for preventing spam and ensuring email authenticity.
Technical article
Documentation from Mailgun explains how reverse DNS (rDNS) can be used for white labeling email sending. This practice helps to promote brand recognition and improve overall deliverability by presenting a more professional sending identity.
Related resources
11 resources
Related pages
What is the best practice for reverse DNS resolution when sending email via an ESP?
Do PTR records and HELOs impact email deliverability?
How does missing or different reverse DNS (rDNS) impact email deliverability, and when is a dedicated IP address needed?
Why is reverse DNS important for email sending?
How does rDNS impact email deliverability when using dedicated IPs?
Email Deliverability Issues: Getting Your Messages to the Inbox in 2025
What is a DNSBL and how does it affect email deliverability?
An in-depth guide to email blocklists
Why Your Emails Are Going to Spam in 2024 and How to Fix It
