Summary
RoadRunner (now part of Spectrum/Charter Communications) deferrals and rejections, specifically errors like 421 4.4.0 [internal] no mail servers for this domain could be reached at this time and 550 5.1.0 ...@... sender rejected. AUP#In-1310, can be puzzling even for senders with excellent reputations. These issues often stem from a combination of factors related to recipient domain status, aggressive filtering by spam protection services like Proofpoint and Cloudmark, and underlying list hygiene problems.
Key findings
- Filtering systems: Time Warner Cable (TWC), the parent company of RoadRunner, utilizes Proofpoint and Cloudmark for their email filtering and rate limiting decisions.
- Internal deferrals: The 421 4.4.0 [internal] error often indicates a 'fake' bounce from the Mail Transfer Agent (MTA). This typically means there are no reachable MX (Mail Exchange) records for the recipient domain or the associated IPs are unreachable.
- Sender rejections: The 550 5.1.0 sender rejected. AUP#In-1310 code points to a specific block against the sender, often related to an Acceptable Use Policy (AUP) violation.
- Deprecated domains: Many rr.com domains were deprecated years ago, leading to a high number of stale or invalid addresses that haven't been adequately pruned from sender lists.
- List hygiene: Persistent deferrals and rejections for a sender, even those perceived as reputable, can signal underlying issues with data collection and list management practices, such as a lack of proper opt-in or significant numbers of dead addresses.
Key considerations
- MX record verification: For 421 4.4.0 [internal] errors, confirm that the recipient domains have valid and reachable MX records. This can be done by attempting to send mail from other sources to those domains.
- List cleansing: Aggressively prune old or deprecated addresses, especially those related to rr.com or similar legacy domains. Improving list hygiene is crucial for improving deliverability. For more information, read about why some emails to Road Runner domains experience delivery issues.
- Understanding rejections: A 550 5.1.0 rejection means a direct block. This requires a thorough review of sending practices and content to identify the specific AUP violation. This could be related to what causes sender rejection errors and low reputation bounces.
- Postmaster contact: Direct contact with RoadRunner/Spectrum postmaster services can be challenging. Escalating issues to Proofpoint or Cloudmark directly may be more effective for resolving specific blocks or rate limits, but only after internal factors have been ruled out.
What email marketers say
Email marketers often face consistent challenges with RoadRunner (Spectrum/Charter) email deliverability, even when maintaining good sending practices. Many report that these providers are notoriously difficult to work with due to a perceived lack of accessible postmaster support and aggressive filtering by third-party services like Proofpoint and Cloudmark. The consensus suggests a need for vigilant list hygiene and understanding the nuances of these cable-based ISPs.
Key opinions
- Persistent issues: Many marketers report ongoing issues with RoadRunner, even for senders who follow best practices and maintain good sender habits.
- Lack of support: A common complaint is the difficulty in contacting a true postmaster or support channel for these cable-based email providers to address deliverability problems.
- Filtering complexities: Marketers recognize that RoadRunner leverages services like Proofpoint and Cloudmark, which apply specific rate limits and filtering decisions that can impact even reputable senders. Understanding email deliverability issues is key.
- Root cause analysis: Before escalating to third-party filters, marketers suggest eliminating internal factors, such as poor list hygiene or other data management problems, as the cause of deferrals and rejections.
Key considerations
- Holistic approach: Even with reputable traffic, deliverability to RoadRunner requires ongoing monitoring and potentially adjusting sending patterns or content to align with their filtering systems.
- Internal troubleshooting: Prioritize diagnosing and resolving internal issues related to email list quality or sending infrastructure before seeking external assistance from Proofpoint or Cloudmark.
- Adaptation: Be prepared for the unique challenges presented by cable-based ISPs like RoadRunner, which may not offer the same level of transparency or direct support as other major mailbox providers. Understanding why your emails fail can help.
- Community insights: Leverage insights from deliverability communities and forums to understand common patterns and solutions for RoadRunner-specific issues.
Marketer view
Email marketer from Email Geeks indicates they consistently encounter difficulties with RoadRunner, even when dealing with senders who adhere to excellent email sending practices. This suggests that the issues might not always be attributed to sender reputation but could be systemic with the receiving end. Maintaining a strong sender reputation is often not enough to guarantee smooth delivery to these domains.
Marketer view
Email marketer from Email Geeks explains their ongoing struggle with cable-based email providers like RoadRunner, primarily due to the significant challenge of finding and contacting a functional postmaster. This lack of a direct communication channel makes resolving deliverability issues exceptionally difficult for senders, leading to prolonged problems and limited recourse for investigation.
What the experts say
Experts in email deliverability confirm that RoadRunner (Charter/Spectrum) is a challenging mailbox provider, heavily relying on third-party anti-spam services like Proofpoint and Cloudmark. They emphasize that specific deferral and rejection codes, such as those indicating unreachable mail servers or AUP violations, often point to deeper issues related to sender data quality and list hygiene. The deprecation of rr.com domains years ago continues to be a major factor in problematic recipient lists.
Key opinions
- Reliance on external filters: RoadRunner's filtering decisions, including rate limits, are significantly influenced by Proofpoint and Cloudmark. These services are key determinants of whether mail is deferred or rejected.
- Fake bounces: The 421 4.4.0 [internal] no mail servers for this domain could be reached message is often a 'fake' bounce generated by the MTA. It indicates that the recipient domain's MX records are either non-existent or pointing to unreachable servers.
- Specific sender blocks: A 550 5.1.0 sender rejected message signifies a direct, specific block against the sender, often triggered by a clear AUP violation, or very strong negative signals about the sender. Ensuring proper email authentication like DMARC, SPF, and DKIM can help mitigate this, as outlined in a simple guide to DMARC, SPF, and DKIM.
- Data quality issues: High rates of these errors suggest significant problems with the sender's data collection and management, including a large number of dead addresses from deprecated domains (like rr.com) and other signals indicating non-opt-in practices. Learn how to boost email deliverability rates.
Key considerations
- Verify recipient status: For domains experiencing [internal] bounces, confirm that the domains are still active and have correct MX records. Sending test emails to these addresses through different sources can help validate their status.
- Improve list hygiene: Aggressively clean email lists to remove invalid, inactive, or deprecated addresses. This reduces the number of bounces and helps improve sender reputation with filtering services.
- Address AUP violations: If encountering AUP-related rejections, review the content, sending frequency, and subscriber acquisition methods to identify and rectify practices that might be violating acceptable use policies.
- Engage third-party support cautiously: While contacting Proofpoint or Cloudmark can be helpful, it should be done after a thorough internal audit confirms that the sender's practices are sound. Escalation without addressing underlying issues may not yield positive results.
Expert view
Email expert from Email Geeks confirms that Time Warner Cable (TWC), now Spectrum, uses both Proofpoint and Cloudmark for their email filtering decisions. This means that any deferrals or rate limits experienced are often a direct result of policies and algorithms implemented by these anti-spam vendors. Senders should understand that resolving issues with RoadRunner often involves understanding how these third-party services operate.
Expert view
Email expert from Email Geeks clarifies that the [internal] component in the 421 4.4.0 bounce is a 'fake' bounce generated by the Mail Transfer Agent (MTA). This means the issue isn't necessarily with the recipient's mailbox being full, but rather an inability to reach the mail servers for that domain. It suggests a problem with the domain's MX records or the reachability of its associated IPs.
What the documentation says
Official documentation from email providers and anti-spam services consistently highlights the importance of adhering to email standards, maintaining high sender reputation, and vigilant list management to ensure deliverability. While specific RoadRunner documentation may be limited, the general principles espoused by filtering solutions like Proofpoint and Cloudmark provide insight into why deferrals and rejections occur. These often relate to perceived violations of acceptable use policies, invalid recipient addresses, or exceeding established rate limits.
Key findings
- Bounce code interpretation: Standard SMTP (Simple Mail Transfer Protocol) response codes like 4XX (deferrals) and 5XX (rejections) indicate temporary or permanent delivery failures, respectively. The specific sub-codes provide more context on the reason.
- Sender reputation metrics: ISPs and anti-spam services evaluate sender reputation based on multiple factors, including complaint rates, unknown user rates (bounces), spam trap hits, and authentication records (SPF, DKIM, DMARC).
- Acceptable use policies (AUPs): Rejections often occur due to violations of an ISP's AUP, which can include sending unsolicited mail, having high bounce rates, or engaging in practices that resemble spamming, even if unintended.
- Role of DNS records: Properly configured MX records are essential for mail routing. An inability to reach mail servers for a domain can lead to deferrals. What is a DNSBL and how does it affect email deliverability.
- Blocklist impact: Inclusion on public or private blacklists (blocklists) can directly result in email rejections. Services like Cloudmark contribute data to these lists. Understanding what happens when your domain is on an email blacklist is critical.
Key considerations
- Monitor bounce rates: Regularly analyze bounce logs and categorizing them by type and recipient domain is crucial. High unknown user rates are a red flag for most ISPs.
- Implement strong list management: Maintain opt-in processes rigorously and promptly remove unengaged or invalid addresses to prevent future deliverability issues.
- Verify recipient domains: Before sending, check if recipient domains are still active and have valid mail exchange (MX) records. Tools for MX lookup can assist here.
- Review sending practices against AUPs: Familiarize yourself with common ISP acceptable use policies to avoid triggering rejections, especially concerning content and sending volume.
Technical article
RFC 5321 (SMTP) documentation details the standard response codes for email delivery. It states that 4XX codes indicate a transient negative completion reply, meaning the mail command was not accepted, but the error condition is temporary. Senders should attempt to resend the mail at a later time. This standard guides how mail servers communicate delivery issues, requiring senders to retry deferred messages responsibly.
Technical article
Proofpoint documentation explains that their email security solutions leverage a multi-layered approach to detect and block threats, including spam, phishing, and malware. Their filters analyze various attributes of an email, such as sender reputation, content, and attachments, to make filtering decisions. Rate limiting, a common cause of deferrals, is applied when sending behavior exceeds predefined thresholds, even for otherwise legitimate mail flows.
Related pages
Why are some emails to Road Runner domains experiencing delivery issues such as delays and bounces?
What causes sender rejection errors and low reputation bounces, particularly with Yahoo, and how can they be resolved?
Why are my IP ranges facing deferred issues in Proofpoint?
Why are my emails delayed even with a good reputation and no errors?
An in-depth guide to email blocklists
How email blacklists actually work: a simple guide
Spam traps: what they are and how they work
A practical guide to understanding your email domain reputation
Email Deliverability Issues: Getting Your Messages to the Inbox in 2025
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