Why is reverse DNS important for email sending?

Key findings

• Mandatory for major providers: Leading mailbox providers like Yahoo and Google now require all senders, regardless of size, to have valid reverse DNS configured for their sending IPs. This makes it an urgent issue for anyone involved in email sending.
• Verification of legitimacy: rDNS, especially when forward-confirmed (FCrDNS), proves that the domain owner and the IP owner are cooperating. This signals to receiving servers that the email originates from a legitimate source, not a compromised server or spam bot.
• Impact on deliverability: Mailbox providers often prefer, or even require, that incoming mail originates from IP addresses with valid reverse DNS. Failure to meet this expectation can lead to emails being rejected, deferred, or routed directly to the spam folder, diminishing your email deliverability.
• Reputation building: A properly configured rDNS helps map hostname-based reputation to IP-based reputation, contributing positively to your sender score and trustworthiness.

Key considerations

• ESP responsibility: If you are sending email through an Email Service Provider (ESP) like Hubspot, they are typically responsible for configuring or providing the means to configure reverse DNS for the shared or dedicated IPs you use. You should consult their support or documentation for guidance on their best practices for reverse DNS resolution with their platform.
• FCrDNS is key: For the strongest authentication, ensure that your reverse DNS setup facilitates FCrDNS, meaning both the forward and reverse lookups resolve consistently. This establishes a high level of trust.
• Troubleshooting tools: Tools that check your email configuration, such as AboutMyEmail, can help identify if your reverse DNS is correctly configured. While occasional transient DNS errors can occur, consistent reporting of missing rDNS should be addressed promptly.
• Dedicated vs. shared IPs: The management of rDNS can differ depending on whether you use a dedicated IP address or a shared IP. Understanding your setup is crucial. More information on this can be found at Mailgun's blog on rDNS white labeling.

Key opinions

• ESP responsibility: Many marketers believe that their ESP should handle the technical setup of rDNS, especially when using their shared infrastructure, as documented in our article on shared rDNS issues for SaaS platforms.
• Direct impact on deliverability: Marketers frequently recognize that missing or incorrect rDNS directly leads to emails being blocked or landing in spam folders, affecting campaign performance.
• Confusion over configuration: There's often confusion and frustration regarding how to configure rDNS, particularly when ESP documentation is not clear or readily available.
• Importance of clear explanations: Marketers express a strong desire for simple, non-technical explanations of complex DNS concepts like rDNS and PTR records, to better understand their significance.

Key considerations

• Prioritize rDNS setup: Given its impact on deliverability, marketers should treat rDNS configuration as a high-priority item for their email sending infrastructure.
• Engage with ESP support: If you're using an ESP and facing rDNS issues, proactively contact their support team for clarification and assistance with configuration.
• Utilize testing tools: Regularly use email testing tools (such as those found at AboutMyEmail) to verify your rDNS setup and ensure it is consistently resolving correctly.
• Understand technical requirements: Even if an ESP handles it, a basic understanding of what PTR records are and their role in rDNS can help marketers troubleshoot and communicate effectively with technical teams.

Key opinions

• Trust signal: Experts agree that valid rDNS serves as a crucial trust signal for mailbox providers, indicating that the sending server is legitimate and authorized.
• Bidirectional mapping: The core function of rDNS is to map an IP address back to a hostname, while FCrDNS extends this by ensuring a consistent, bidirectional match between the IP and its associated domain. This is essential for proper PTR record and HELO configuration.
• Reputation alignment: Proper rDNS allows for the effective mapping of hostname-based reputation to IP-based reputation, which is important for how filtering systems assess incoming mail.
• Anti-spam measure: rDNS helps identify and deter fraudulent or compromised sending sources, contributing to overall network security and spam prevention.

Key considerations

• Configuration accuracy: Ensuring your A record maps to the IP and the PTR record maps back to the domain (the 'A to B to A' loop) is crucial for valid rDNS and FCrDNS.
• Proactive monitoring: Regularly verify rDNS configuration, as transient DNS errors can sometimes cause false negatives in testing tools.
• Impact on blocklists: Missing or misconfigured rDNS can contribute to an IP address being added to an email blacklist or blocklist, further harming deliverability.
• Technical resource: For a deeper dive, SpamResource offers additional insights into what DNSBLs are and how they operate in relation to rDNS.

Key findings

• Security measure: Reverse DNS lookup is frequently used by receiving email servers as a security measure to verify the source of incoming email.
• IP to domain mapping: It allows mail servers to conduct anti-spam checks by matching an IP address to a domain name, essentially performing a reversed DNS lookup.
• Authentication component: PTR DNS records are part of the overall email authentication process, ensuring the sending IP has a valid reverse DNS entry.
• Impact on deliverability: Having a valid reverse DNS record for an email server is considered essential for maintaining email deliverability and preventing mail from being marked as spam.

Key considerations

• Consistent records: Proper configuration involves ensuring that the A record for the hostname resolves to the IP address, and the PTR record for the IP address resolves back to the same hostname, forming a consistent loop.
• Compliance with standards: While RFCs might not strictly require rDNS for all mail servers, many industry best practices and mailbox provider policies enforce it as a prerequisite for good sending reputation.
• Managed by IP owner: The PTR record (rDNS entry) for an IP address is typically managed by the owner of the IP block, which is often your internet service provider or hosting company.
• Improves security and logging: Beyond email, reverse DNS also contributes to improved network security and logging accuracy, as detailed in JumpCloud's explanation of rDNS.