How does rDNS impact email deliverability when using dedicated IPs?

Key findings

• Indirect impact: While a mismatched or unaligned rDNS may not directly block emails, it can be one of several factors that cumulatively reduce email deliverability.
• Stricter filters: B2B environments and specific mailbox providers (like Proofpoint or some European ISPs) are more likely to scrutinize rDNS alignment, potentially leading to emails being filtered or rejected.
• FCrDNS validity: The critical factor is often not who the rDNS points to, but that the IP address resolves to a hostname, and that hostname then resolves back to the original IP address. This is known as forward-confirmed reverse DNS, or FCrDNS. Learn more about what is reverse DNS and its impact.
• Reputation dependency: If the ESP's domain used in rDNS has a poor reputation (e.g., due to association with spammers), it can negatively affect the client's deliverability. Consider maintaining dedicated IP reputation.
• Dynamic records: Some mail receivers are suspicious of rDNS records that appear to be dynamically assigned or frequently change.

Key considerations

• White-labeling for branding: Aligning rDNS to the client's domain provides complete brand control and removes any trace of the ESP in email headers. This is primarily a branding choice rather than a strict technical requirement for deliverability.
• DNS management: If rDNS points to the client's domain, the client is responsible for maintaining the corresponding A record, and misconfigurations can impact delivery. Delegating a subdomain to the ESP can simplify management while allowing for a degree of branding, as discussed by Mailgun in their reverse DNS white-labeling article.
• Proactive best practice: Even if not strictly required, setting up rDNS to align with your sending domain is a best practice that supports better sender reputation and helps avoid potential deliverability problems down the line.
• Consistency: Maintain a consistent and unambiguous naming convention for your rDNS records. Avoid anything that might appear generic or suspicious to receiving mail servers.

Key opinions

• Minimal standalone impact: Many marketers report that unaligned rDNS (where the PTR points to the ESP's domain) does not cause massive, isolated deliverability issues. It's often viewed as a contributing factor rather than a sole cause of problems.
• B2B sensitivity: There's a consensus that B2B receivers, particularly those using advanced spam filters, are more sensitive to rDNS alignment.
• ESP reputation matters: The reputation of the domain that the rDNS points to is crucial. If the ESP's domain (used in rDNS) has a bad reputation due to lax terms of business or problematic senders, it can indeed lead to deliverability issues for the client.
• Branding preference: The primary driver for white-label rDNS (pointing to the client's domain) is often to ensure no trace of any brand not theirs appears in email headers, rather than a purely technical deliverability requirement.

Key considerations

• Proactive alignment: Even if its individual impact is debatable, aligning rDNS to the client's domain is seen as a positive step for overall sender reputation and best practice. You can also explore how SPF, DKIM, and DMARC affect deliverability when using a third-party ESP.
• DNS delegation: Delegating a subdomain for rDNS back to the ESP can reduce maintenance overhead, but some clients may prefer not to relinquish DNS control.
• Holistic deliverability: Marketers recognize that rDNS is one piece of a larger deliverability puzzle. Issues often arise from a combination of multiple red flags rather than a single misconfiguration. As SendGrid highlights, proper reverse DNS setup is among the steps after getting a dedicated IP address.

Key opinions

• FCrDNS is key: The critical aspect is that the IP address correctly resolves to a hostname (PTR record), and that hostname then resolves back to the same IP address (A record). As long as this FCrDNS check passes, the specific domain (ESP's or client's) is often less important than its validity.
• Reputation of rDNS domain: Issues primarily arise if the domain used in the rDNS record has a poor or compromised reputation. This emphasizes why DNS server reputation affects deliverability.
• Dynamic records are suspicious: Mail receivers can treat rDNS records that appear dynamic with suspicion, highlighting the need for stable and identifiable records.
• Specific MBP requirements: Some mailbox providers, like T-Online.de, may have unstated preferences or stricter interpretations of rDNS requirements, sometimes appearing to almost require a non-default rDNS for high-volume senders, though this is not a universal explicit requirement.

Key considerations

• Client control vs. ESP management: While white-label rDNS is desirable for branding, it places DNS update responsibility on the client. Delegating a subdomain to the ESP can mitigate this, balancing control and ease of management.
• Consistency and clarity: Regardless of who manages it, the rDNS naming convention should be consistent and unambiguous. For further context, understand how important rDNS matching SMTP banners is.
• Holistic deliverability strategy: rDNS is one of many signals. A robust deliverability strategy requires proper authentication (SPF, DKIM, DMARC), good list hygiene, and consistent sending patterns. Learn about missing reverse DNS impact for email.

Key findings

• Sender verification: Documentation consistently states that rDNS allows mailbox providers to verify the sender by performing a reverse DNS lookup upon email receipt. This is a critical step in establishing trust.
• Spam prevention: Many receiving mail servers will reject or flag incoming messages from IP addresses that lack a proper rDNS record, specifically to deter spammers who often do not bother with such configurations.
• FCrDNS importance: The requirement for a valid reverse DNS often implies the necessity of forward-confirmed reverse DNS (FCrDNS), where the IP points to a hostname, and that hostname points back to the same IP. This ensures a consistent and verifiable sender identity.
• Dedicated IP benefit: For dedicated IPs, setting up rDNS allows the sender to control their own reputation and avoid being influenced by other users sharing an IP, as highlighted by SendGrid in their guide on email deliverability with shared IP pools.

Key considerations

• Pre-configured rDNS: Some ESPs or cloud providers like AWS confirm that their dedicated IPs come pre-configured with proper rDNS, which should be sufficient to prevent delivery issues. For more details, consult AWS's guidance on rDNS for dedicated IPs.
• Alignment with sender guidelines: Official guidelines, such as Google's sender requirements, implicitly rely on correct rDNS setup for IP reputation and overall deliverability, particularly for high-volume senders.
• Consistent naming: While not always requiring custom rDNS, providers often value a consistent and unambiguous naming convention for the rDNS record to ensure clear sender identification.
• Complementary authentication: rDNS is part of a broader email authentication framework that includes SPF, DKIM, and DMARC. Proper configuration of all these elements is crucial for optimal deliverability.