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What is reverse DNS (rDNS) and FCrDNS, and how do they impact email sending?

Summary

Reverse DNS (rDNS) is a crucial component of email deliverability, acting as the inverse of standard DNS. While forward DNS (A records) translates a domain name into an IP address, rDNS (specifically, PTR records) translates an IP address back into a domain name. FCrDNS, or Forward-Confirmed Reverse DNS, takes this a step further by requiring that the rDNS lookup (IP to domain) matches the forward DNS lookup (domain to IP). This dual verification process is widely used by receiving mail servers to authenticate sending servers, significantly impacting whether your emails land in the inbox or are flagged as spam.

What email marketers say

Email marketers often find the technical aspects of rDNS and FCrDNS daunting, usually expecting their Email Service Providers (ESPs) to handle these configurations. However, issues can arise, especially when using specific email setups or monitoring tools that flag potential rDNS problems. Marketers are primarily concerned with the direct impact on their email campaigns and sender reputation, seeking clarity on who is responsible for these technical configurations.

Marketer view

Email marketer from Email Geeks asked about the Reverse DNS (PTR) record requirement, stating they hadn't fully understood it yet and were seeking clarification.

22 Jan 2024 - Email Geeks

Marketer view

Email marketer from Campaign Cleaner highlights that a server's reverse DNS must match its forward DNS, otherwise mismatches can lead to emails being flagged as suspicious or rejected.

25 Feb 2023 - Campaign Cleaner

What the experts say

Experts consistently emphasize that Forward-Confirmed Reverse DNS (FCrDNS) is a non-negotiable requirement for legitimate mail servers. They highlight that the absence or misconfiguration of rDNS, particularly generic rDNS entries, serves as a strong indicator of a non-standard or potentially malicious sending source. For most businesses leveraging ESPs, rDNS management falls squarely on the provider, but self-hosters or those with dedicated IPs must ensure proper setup to maintain deliverability.

Expert view

Expert from Email Geeks states that your email or CRM provider should handle reverse DNS (rDNS), as the requirement is that sending MTAs (email servers) have Forward-Confirmed Reverse DNS (FCrDNS).

22 Jan 2024 - Email Geeks

Expert view

Expert from SpamResource explains that proper rDNS configuration is one of the foundational elements of good email deliverability, and its absence can cause legitimate emails to be treated as spam.

10 Mar 2024 - SpamResource

What the documentation says

Official documentation and industry standards highlight reverse DNS and FCrDNS as fundamental aspects of email server configuration for security, logging, and anti-spam measures. RFCs and prominent mail service providers (ISPs) often implicitly or explicitly require these checks. The core principle is to verify the identity of the sending server, ensuring that the IP address corresponds to a legitimate hostname. Failure to meet these expectations can lead to emails being rejected or classified as spam, impacting deliverability significantly.

Technical article

Documentation from JumpCloud states that reverse DNS improves network security, logging accuracy, and email authentication, and is frequently employed to verify server identities prior to email transmission.

15 Sep 2023 - JumpCloud

Technical article

ClouDNS Blog documentation confirms that Reverse DNS significantly impacts email deliverability because many mail servers use rDNS to verify the sender's legitimacy upon receiving an email.

10 Jan 2023 - ClouDNS Blog

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