Resolving email servers can be challenging, especially when encountering the phrase “Reverse DNS does not match SMTP Banner.” This pop-up message has concerned the administrators.
According to data gathered from the first few months of 2023, around 40% of the malicious emails received by the users were either response-based attacks or email impersonation attacks.
These attacks can be leveraged for various reasons. Mismatched rDNS and SMTP Banner are two examples. This error must be tackled effectively to maintain effective email communication.
Understanding the components causing this issue and the steps needed to resolve it is essential. In this article, you will learn what the phrase “Reverse DNS does not match SMTP Banner” means and how to fix it.
About Reverse DNS
In standard DNS, the user finds the IP address when the domain name is already given. However, as the name indicates, reverse DNS is the opposite of standard DNS. In reverse DNS, the user already has an IP address, which is then used to search for a domain name.
The Internet Engineering Task Force states that every domain should support reverse DNS. However, reverse DNS is optional for the Internet; only some domains use it. Implementing reverse DNS helps in network troubleshooting and security enhancement.
What Are SMTP Banners?
An SMTP Banner is an initial response an email server gets when it connects to an Exchange server. The banner appears when the messaging server connects to a receiver on the exchange server. The SMTP Banner contains the required information about the server, including the hostname, which is essential for maintaining email communication
These Banners also display certain information that can help with troubleshooting, which is useful in diagnosing issues with email delivery. Administers can often customise the SMTP Banner to display or hide certain information for security reasons.
Why Must rDNS Match with SMTP Banner?
Reverse DNS is vital for email delivery. If it doesn’t align with the SMTP Barrier, it can cause email delivery and filtering failures, threatening email security. To enhance email communication, reverse DNS must match the hostname in the SMTP Barrier.
Any misalignment between both can affect email services by threatening spam filtering. Most email systems don’t wholly reject emails with an rDNS mismatch, but there are chances for these emails to be marked as spam. Therefore, the mismatch must be fixed to ensure smooth mail delivery.
Email spam filters are designed to spot signs of any suspicious activity. One of those signs is a mismatch between Reverse DNS and the SMTP Banner. If this mismatch persists without being resolved, your domain’s IP address might be blacklisted.
Reasons Behind The Mismatch
Various factors can cause a mismatch between Reverse DNS and SMTP. Here are a few common issues that need to be addressed.
Issues In SMTP Server Settings
The reverse DNS and SMTP mismatch can arise from outdated and incorrect SMTP server settings. It can happen because of domain name changes, server migrations, or disoriented setups. Therefore, performing a regular server check and regularly updating the settings can prevent this.
Misconfigured DNS Records
The most common cause of a mismatch with SMTP Banners is a misconfigured DNS record. However, human errors or misinterpretation of instructions can also cause a mismatch.
It can also be caused by not regularly updating the records after host changes. If delays in the update cause the mismatch, regular auditing of DNS records is needed to help identify and fix errors.
Hosting Multiple Domains on One IP Address
It happens when multiple domains share a single IP address. One domain’s SMTP barrier might be used for another’s Reverse DNS lookup.
It can lead to a mismatch even if an individual domain settings are correct. This can be resolved by adequately pairing each domain’s SMTP Banner and reverse DNS.
Troubleshooting Reverse DNS and SMTP Banner Mismatch
It is essential to analyze and promptly resolve the reverse DNS and SMTP Banner mismatch issue. The problem can be resolved by following the steps and strategies mentioned below.
Review Mail Server Configuration
First, check your mail server’s configuration to confirm that the reverse IP address is correctly represented in the server barrier. Adjust the configuration settings by preparing the SMTP banner to match the reverse DNS.
Run Thorough DNS Checks
Verifying the MX records is crucial. You must confirm that your domain has the correct MX records pointing to the mail server. Check the PTR Record carefully. It must accurately link the IP address with the mail server hostname.
Adjusting SMTP Server Settings
You can check your current SMTP banner by accessing the SMTP server’s configuration. The settings must match the domain name specified in the DNS settings. If the SMTP Banner is incorrect, modify it to match the expected domain name. The process will vary depending on the email server software.
Enhance Authentication
Email authentication protocols, like DMARC, can also indirectly help address the issue with enhanced security. As DMARC builds on existing protocols like SPF and DKIM, it can resolve various email-related issues. The detailed reports on email-sending practices highlight the configuration problems and rectify them.
Test SMTP Banner Changes
After making configuration adjustments, you can also use an SMTP Diagnostic Tool to test and confirm whether the reverse DNS matches with the SMTP Banner or not. You must ensure that the change has taken effect and resolve concerns about the mismatch.
Verification
Send test emails to different service providers to ensure they are delivered without issues. Run tools like MXToolbox to verify that the SMTP banner now matches the Reverse DNS. Send a test email to yourself and inspect the headers to check warning signs related to the SMTP banner.
Conclusion
Overcoming challenges like the “Reverse DNS does not match SMTP Banner” issue can be worrisome. However, the problem can be tackled easily by following the steps mentioned above. Understanding the root cause and implementing the recommended solutions is essential.
In addition to technical adjustments, email server configurations are also crucial. Regular updates and auditing server techniques can prevent mismatches. PowerDMARC can help users implement email authentication protocols. This approach helps safeguard communication channels and strengthen overall security.