Summary
A generic RDNS is a significant factor leading to Spamhaus blacklisting due to the perception by automated systems that it's associated with dynamic IPs, home users, and spammers. It can be a false positive, but a less complex hostname is recommended. Dynamic RDNS negatively impacts deliverability, as ISPs view it suspiciously, associating it with compromised machines. A proper, static RDNS record matching the hostname to the A record is crucial for trust and deliverability. Missing or generic RDNS also indicates potential spam activity, obscuring organizational identity and harming reputation, leading mail servers to reject emails. Blocklisting is triggered by IP reputation issues related to generic RDNS, including spam traps, complaints, or spam-like activity.
Key findings
- Generic Hostname: Generic hostnames trigger automated spam detection systems.
- Dynamic IP Association: Generic RDNS is associated with dynamic IPs used by spammers.
- Static IP Required: A static IP with a matching PTR record is crucial for deliverability.
- rDNS Matching: The RDNS record should resolve to the same hostname as the A record.
- Reputation Impact: Generic/missing RDNS negatively impacts sending reputation.
- Obscured Identity: Generic RDNS obscures organizational identity.
- Blocklisting Factors: IP reputation issues, spam traps, complaints, and spam-like activity all contribute.
Key considerations
- Simplify Hostname: Use a less convoluted hostname.
- Static IP: Switch to a static IP address.
- Configure PTR: Configure a PTR record matching your domain name.
- Monitor Reputation: Monitor your IP and domain reputation regularly.
- Proper RDNS: Ensure your mail server has a proper, domain-specific RDNS record.
- Avoid Dynamic IPs: Avoid using dynamic IP addresses for sending email.
- Review Practices: Ensure sending practices aren't triggering spam filters or complaints.
What email marketers say
5 marketer opinions
A generic or dynamic RDNS (Reverse DNS) record is a common reason for an IP address to be blacklisted by Spamhaus and other blocklist providers. This is because generic RDNS records are often associated with dynamic IP addresses assigned by ISPs, which are frequently used by spammers or compromised machines. A properly configured, static RDNS record that matches the hostname of the mail server is crucial for establishing trust with ISPs and email providers, and for improving email deliverability. Mismatched or missing RDNS records can flag an IP address as potentially malicious.
Key opinions
- Negative Impact: Dynamic RDNS negatively impacts email deliverability.
- Suspicious Activity: ISPs view dynamic RDNS as suspicious, associating it with spam.
- A Record Matching: RDNS should resolve to the same hostname as the A record.
- Distrusted by Mail Servers: Mail servers distrust generic RDNS due to frequent use for spam.
- Legitimacy Signal: Domain-specific RDNS indicates a legitimate mail server.
- Blacklist Reason: Generic RDNS is a frequent reason for blacklisting.
Key considerations
- Static RDNS: Implement a static RDNS record for your mail server.
- Proper Configuration: Ensure RDNS matches the hostname of your mail server.
- Monitor Reputation: Regularly check your IP address on blocklists and monitor your sending reputation.
- Contact ISP: If using dynamic IP, consider contacting your ISP for a static IP or explore alternative sending solutions.
Marketer view
Email marketer from ServerFault shares that the rDNS record (reverse DNS) should resolve to the same hostname as the A record, which means the IP address and host name should match. If the hostname does not resolve to the same IP address, it could be flagged as spam.
15 Apr 2022 - ServerFault (Stackoverflow)
Marketer view
Email marketer from cPanel Forums explains that using a generic RDNS (like one assigned by your ISP) can lead to deliverability problems. A proper, domain-specific RDNS is seen as a sign of a legitimate mail server.
18 Mar 2022 - cPanel Forums
What the experts say
4 expert opinions
A generic RDNS can lead to Spamhaus blacklisting because it appears generic to automated systems, raising suspicion. While sometimes a false positive that Spamhaus will correct, a less complex hostname is advisable. Blocklisting stems from IP reputation issues linked to generic RDNS, triggered by spam traps, complaints, or spam-like activity. The rDNS identifies the email source and affects sending reputation; a generic or missing rDNS harms deliverability as it obscures organizational identity.
Key opinions
- Generic Hostname: Generic-looking hostnames trigger automated spam detection.
- False Positive: Blacklisting can be a false positive with generic RDNS.
- IP Reputation: Generic RDNS contributes to negative IP reputation.
- Source Identification: rDNS helps identify the email source, impacting reputation.
- Obscured Identity: Generic/missing rDNS obscures the organization's identity.
Key considerations
- Simplify Hostname: Consider using a less convoluted hostname.
- Monitor Reputation: Regularly monitor your IP and domain reputation.
- Review Sending Practices: Ensure your sending practices are not triggering spam filters or complaints.
- Clear Identification: Maintain a clear rDNS that identifies your organization or infrastructure.
Expert view
Expert from Email Geeks shares that it’s a false positive, which spamhaus will fix, but suggests moving to something a bit less convoluted.
8 Apr 2023 - Email Geeks
Expert view
Expert from Spam Resource explains that the rDNS helps identify the source of an email and impacts your sending reputation. Generic or missing rDNS records can negatively impact your email deliverability and may contribute to blacklisting because they don't clearly identify your organization or infrastructure.
1 Nov 2024 - Spam Resource
What the documentation says
3 technical articles
Spamhaus, Microsoft, and Hetzner documentation indicate that dynamic or generic RDNS records often lead to blacklisting because they are commonly associated with home users, small businesses with dynamic IPs, and spammers. Static IP addresses with valid, matching PTR records are crucial for email deliverability, as dynamic IPs and missing/generic rDNS records are often blocked or rejected by mail servers due to their association with spam activities.
Key findings
- Dynamic IP Association: Generic RDNS often indicates dynamic IPs used by home users/small businesses.
- Spammer Association: Dynamic IPs are frequently used by spammers, leading to blacklisting.
- Static IP Requirement: Static IPs with valid PTR records are crucial for sending email.
- Rejection by Mail Servers: Missing or generic rDNS records often result in email rejection.
Key considerations
- Obtain Static IP: Switch to a static IP address for your mail server.
- Configure PTR Record: Set up a valid PTR record that matches your domain name.
- Avoid Dynamic IPs: Avoid using dynamic IP addresses for sending email.
- Ensure Proper rDNS: Ensure your mail server has a proper rDNS record.
Technical article
Documentation from Hetzner.com explains that a missing or generic rDNS record is often used by spammers, so many mail servers reject emails from servers that don't have a matching rDNS record.
2 Dec 2022 - Hetzner.com
Technical article
Documentation from Microsoft.com explains that using static IP addresses with a valid reverse DNS entry (PTR record) that matches the domain name is crucial for sending email. Dynamic IP addresses are often associated with spammers and may be blocked.
29 Apr 2023 - Microsoft.com
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