Summary
Reverse DNS (rDNS) configuration is a crucial element for email deliverability, particularly when distinguishing between shared and dedicated IP addresses. While official documentation from major mailbox providers like Yahoo and Gmail may not explicitly list custom rDNS as a hard requirement, industry experts and marketers widely consider it a best practice. Proper rDNS helps receiving mail servers verify the legitimacy of incoming email, contributing to a sender's overall reputation and inbox placement. The key is transparency and clear identification of the sending entity, whether it's an Email Service Provider (ESP) or the sender themselves.
Key findings
- Shared IP rDNS: For shared IP pools, the reverse DNS should clearly identify the Email Service Provider (ESP) responsible for the sending infrastructure.
- Dedicated IP rDNS: On a dedicated IP, the rDNS can identify either the ESP or the sender directly. The latter is often preferred for branding and control over sender reputation.
- Avoid IP addresses in rDNS: Reverse DNS hostnames should not contain the IP address itself (e.g., 10.11.12.13.ec2.aws.amazon.com or static-10-11-12-13.shittyvps.ovh.com), as this is often a sign of poor configuration or spammy practices.
- Spammy ESP identification: A common indicator of a questionable ESP is when their reverse DNS domain does not resolve to their official website or an identifiable sender page. If it leads to an unsubscribe form or unrelated content, it's a red flag.
- Responsible party: It should always be easy to identify a responsible party (either the ESP or the sender) from the reverse DNS record.
Key considerations
- Custom rDNS for dedicated IPs: If you are paying for a dedicated IP, your ESP should ideally offer custom reverse DNS as part of the package to enhance your sender reputation.
- Clarity over customisation: While custom rDNS is good, as long as the reverse DNS clearly points to the ESP, it's generally not a deal-breaker for deliverability. Focus on clear identification.
- Impact on deliverability: Missing or improperly configured reverse DNS can negatively impact email deliverability, as it's a key check for mail servers. Learn more about the general topic of reverse DNS and email delivery.
What email marketers say
Email marketers often face practical challenges when dealing with reverse DNS (rDNS) configurations, especially those working with smaller clients or lower-cost Email Service Providers (ESPs). The perceived strength of rDNS requirements from major mailbox providers like Yahoo and Gmail can vary, leading to uncertainty about how strictly these guidelines need to be followed. Marketers frequently navigate the trade-offs between cost, desired features (like custom rDNS), and the volume of email being sent, which often dictates the choice between shared and dedicated IP addresses.
Key opinions
- Challenges with low-cost ESPs: Lower-cost ESPs often do not offer the capability for custom reverse DNS, making it difficult to meet certain best practices.
- Shared IP limitations: When using shared IP addresses due to email volumes, meeting custom rDNS requirements can be practically impossible.
- Strength of requirements: Marketers question how strongly Yahoo and Gmail enforce specific rDNS configurations, especially for smaller senders.
Key considerations
- ESP choice implications: Deciding to switch ESPs (and undergoing a new warm-up process) due to rDNS limitations is a significant decision compared to selecting a new ESP from the start based on their offerings.
- Impact on deliverability for ESPs: Understanding how ESPs impact deliverability on dedicated IPs is crucial. Also consider the basic principles of reverse DNS lookup for email sending.
- Volume vs. Customization: For smaller email volumes, the lack of custom rDNS might not be a major blocker, but it becomes more critical as sending volume and reputation needs grow.
Marketer view
An email marketer from Email Geeks suggests that they push Yahoo and Gmail's best practices on rDNS as strongly as possible, but acknowledge the challenge for smaller customers using lower-cost ESPs, especially with shared IP addresses.
Marketer view
A marketer from Email Geeks inquired about the necessity of custom rDNS for private IPs and whether they should discard an ESP that doesn't offer this feature, indicating a concern for meeting perceived best practices.
What the experts say
Email deliverability experts stress the fundamental role of reverse DNS (rDNS) in establishing sender legitimacy, whether for shared or dedicated IP addresses. They provide clear guidelines on what constitutes a proper rDNS record and how to identify suspicious configurations, often associated with spam operations. While acknowledging that some specific rDNS setups (like white labeling) might not be strictly mandatory, experts consistently emphasize the importance of transparency and accountability in the DNS records to ensure mail servers can reliably identify the sending entity.
Key opinions
- Shared vs. dedicated rDNS: For shared pools, rDNS should identify the ESP, while for dedicated IPs, it can identify either the sender or the ESP.
- Bad rDNS examples: Reverse DNS should never include the IP address itself within the hostname, as this is a strong indicator of poor practice.
- Identifying spammy ESPs: If the organizational domain in the reverse DNS does not lead to a legitimate sender or ESP webpage when visited in a browser, it suggests bad behavior. An unsubscribe page appearing instead is also problematic.
- Not always a deal-breaker: As long as the reverse DNS clearly points to the ESP, even without custom configuration, it is not necessarily a deal-breaker for deliverability, though it might warrant a complaint.
- Responsible party identification: The reverse DNS must make it easy to identify the responsible party, either the ESP or the sender, maintaining transparency.
- What rDNS and FCrDNS are: A full understanding of rDNS and Forward Confirmed reverse DNS (FCrDNS) is critical for email sending.
Key considerations
- Transparency is key: While white labeling may not be mandatory, transparency in rDNS (where the domain links to the ESP or sender) is always beneficial for trust.
- Amazon SES specific: If you are an Amazon SES customer, an rDNS like aXXX.smtp-out.eu-west-1.amazonses.com is acceptable; otherwise, it is not advisable.
- Multi-IP configuration: It is important to understand how to configure rDNS with multiple IP addresses for complex setups. For further expert insights, review industry leader perspectives.
Expert view
An expert from Email Geeks states that if you are sending through a shared pool, the reverse DNS should unequivocally identify the ESP, ensuring proper attribution of mail flow.
Expert view
An expert from Email Geeks clarified that for dedicated IPs, the reverse DNS should identify either the sender or the ESP, offering flexibility while maintaining clear identification.
What the documentation says
Official documentation from major mailbox providers and internet governance bodies provides guidance on reverse DNS (rDNS) to ensure email authentication and combat spam. While specific requirements might vary or evolve, the overarching theme in documentation emphasizes the need for transparent and verifiable sender identification through rDNS. This often involves ensuring that the IP address's pointer (PTR) record resolves to a hostname that clearly identifies the sending entity, be it the sender's domain or their Email Service Provider (ESP).
Key findings
- Yahoo's best practices: Yahoo's sender best practices recommend that the domain used for reverse DNS should be associated with your domain or your ESP's domain.
- General identification expectation: Documentation generally indicates that the reverse DNS should provide a clear and identifiable name for the server sending the email, aiding in reputation assessment.
- PTR records: Reverse DNS relies on PTR records, which map an IP address back to a domain name, acting as the inverse of A records.
- Authentication complement: While not an authentication protocol itself, rDNS works alongside SPF, DKIM, and DMARC to build a complete picture of sender legitimacy for recipient mail servers.
Key considerations
- Official vs. industry practice: While some specific rDNS requirements might not be explicitly mandatory in official documentation, industry best practices often push for a higher standard of configuration for optimal deliverability.
- Importance of transparency: Documentation consistently emphasizes that transparent rDNS configuration is a sign of a legitimate sender, aiding mail servers in filtering out spam and blocklisting (or blacklisting) malicious senders.
- Technical alignment: Ensure your rDNS setup aligns with your other email authentication records like DMARC, SPF, and DKIM. Adherence to sender requirements set by mailbox providers is essential for successful email delivery.
Technical article
Badsender's documentation states that reverse DNS serves as the initial layer of anti-spam filtering, making the rDNS configuration of an IP address crucial for effective email delivery.
Technical article
Mailgun's blog explains that rDNS is important for deliverability, helps avoid common mistakes, and outlines how to set up rDNS records, particularly in the context of reverse DNS white labeling.
Related resources
10 resources
Related pages
What is the best practice for reverse DNS resolution when sending email via an ESP?
How do I configure reverse DNS (rDNS) with multiple IP addresses for email sending?
How does missing or different reverse DNS (rDNS) impact email deliverability, and when is a dedicated IP address needed?
What is reverse DNS (rDNS) and FCrDNS, and how do they impact email sending?
Why is reverse DNS important for email sending?
When should I use a shared IP address over a dedicated IP address for email sending?
How do ESPs impact deliverability on dedicated IPs?
Is shared rDNS an issue for SaaS platforms sending emails on behalf of clients?
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