Why am I seeing RoadRunner deferrals and rejections for reputable senders?
Michael Ko
Co-founder & CEO, Suped
Published 26 Apr 2025
Updated 15 Aug 2025
6 min read
Encountering deferrals and rejections from RoadRunner (Spectrum/Charter) can be perplexing, especially when you maintain a strong sender reputation. It feels counterintuitive when your emails are bouncing back with messages like "421 4.4.0 [internal] no mail servers for this domain could be reached at this time" or "550 5.1.0 ...@... sender rejected. AUP#In-1310," despite your best efforts. I've observed that these issues, even for seemingly reputable senders, often stem from a combination of RoadRunner's specific filtering policies and underlying list hygiene challenges.
Understanding RoadRunner's filtering systems
RoadRunner, now primarily under the Spectrum/Charter umbrella, employs sophisticated email filtering mechanisms. They heavily rely on third-party security services such as Cloudmark and Proofpoint to protect their users from spam and abuse. These systems are known for their aggressive rate limiting and content-based filtering, which can impact even legitimate senders.
The 421 4.4.0 [internal] no mail servers for this domain could be reached at this time error is particularly tricky. While it suggests an issue with the recipient's mail servers, it can often be a fake bounce generated by RoadRunner's mail transfer agent (MTA) itself. This type of deferral often indicates that the recipient's domain might no longer have valid MX records or that their servers are intentionally unreachable to the sender's IP, signaling a potential block. In some cases, it correlates to the ISP's Cloudmark servers putting a sender into a rate-limited "time-out" period, as described by Spam Resource.
Their systems can be quite sensitive to perceived anomalies in sending behavior, which might trigger temporary deferrals. Even with a good overall sender reputation, a sudden spike in volume to their network or a high proportion of invalid addresses on your list can quickly lead to these temporary blocks.
It's important to remember that RoadRunner (Spectrum) postmaster contact information can be hard to find and responses can be slow or non-existent. This makes proactive measures even more critical.
Common causes for deferrals and rejections
A primary cause for these issues, particularly the "550 5.1.0 ...@... sender rejected. AUP#In-1310" error, is often related to poor list hygiene. The AUP#In-1310 code points to an Acceptable Use Policy violation on the inbound side, meaning RoadRunner's filters detected something in the email or sender's behavior that violates their terms.
Many rr.com email addresses are now defunct or converted to other domains under Spectrum. Continuing to send to these old, dead addresses can significantly harm your sender reputation, making your traffic appear suspicious to ISPs. This can lead to your emails being deferred or outright rejected, even if your overall sending practices are sound.
Another factor is how Cloudmark and other filtering services interpret signals from your mail stream. High bounce rates, low engagement (opens/clicks), spam complaints, and hitting spam traps are all strong negative signals. These signals tell the filtering systems that your emails might not be opt-in, leading to specific blocks against your sender.
Best practice: list cleaning
Regularly cleaning your email lists is crucial. Remove inactive subscribers and any addresses that consistently bounce, especially those from old RoadRunner domains. This minimizes the chances of hitting spam traps or sending to invalid addresses, which negatively impact your sender reputation.
Technical and reputational considerations
Beyond list hygiene, technical configurations play a significant role. When you receive a "no mail servers for this domain could be reached" error, it's worth verifying the MX records for those specific recipient domains. Sometimes, the issue might genuinely be on the recipient's end, with misconfigured or unreachable mail servers. You can perform a quick MX record lookup to confirm.
MX record lookup examplebash
dig MX recipientdomain.com
Your domain's sender reputation is a composite score based on many factors. Even if your overall reputation appears good, specific ISPs or filtering services might have their own internal metrics that flag your sending behavior as suspicious. This can happen if, for example, a high percentage of your mail to RoadRunner domains consists of old, unengaged contacts, or if there's a perceived increase in spam complaints from their users. Understanding your domain reputation is key.
Deferral reason
SMTP error:421 4.4.0 [internal] no mail servers for this domain could be reached
Rate limiting or internal block: RoadRunner (often via Cloudmark) temporarily pausing your sending. Could also be genuinely invalid or deprecated rr.com domains.
Sender reputation/list hygiene: Indicates a specific block against the sender due to perceived spammy behavior or poor list quality. Often linked to mailing deprecated rr.com domains.
Strategies for resolution
When facing these RoadRunner deferrals or rejections (also known as a blocklist or blacklist), the first step is to dive deep into your bounce logs. Look for patterns: are the affected recipients consistently from rr.com or other specific domains? Is it always the same error code? This can help you pinpoint whether it's a general issue or specific to certain segments of your list.
Next, prioritize aggressive list cleaning. Any address from a deprecated rr.com domain that consistently bounces should be removed immediately. Beyond that, identify and suppress any addresses that show no engagement over a long period. This proactive approach will help reduce negative signals to ISPs and improve your overall deliverability, especially to stricter receivers. Dealing with deferred email often starts with your list.
Ensure your email authentication records, specifically SPF, DKIM, and DMARC, are correctly configured. Misconfigurations can lead to authentication failures, which are a major red flag for ISPs and can result in rejections. Regularly monitor your DMARC reports for any authentication issues or unusual activity related to your sending domains. You should also regularly check your blocklist status.
Error code
Meaning
Suggested action
421 4.4.0 [internal] no mail servers for this domain could be reached
Temporary deferral, often indicating rate limiting by Cloudmark or genuinely unreachable recipient MX records.
Check recipient MX records. Reduce sending volume and improve list hygiene.
550 5.1.0 ...@... sender rejected. AUP#In-1310
Hard rejection due to an Acceptable Use Policy violation. Often points to specific sender block.
Aggressively clean your list, especially old rr.com domains. Review sending practices for compliance.
Navigating RoadRunner's email landscape
Dealing with RoadRunner (Spectrum/Charter) deferrals and rejections for otherwise reputable senders can be a complex issue, but it's not insurmountable. The key lies in understanding their strict filtering policies, maintaining impeccable list hygiene, ensuring proper technical configurations, and proactively monitoring your email performance. By addressing these areas, you can significantly improve your email deliverability to RoadRunner domains and ensure your messages reach the inbox.
Views from the trenches
Best practices
Maintain an exceptionally clean and engaged email list, especially for older domains.
Segment your audience to tailor content and reduce unengaged sending.
Regularly monitor your bounce logs and DMARC reports for RoadRunner specific errors.
Ensure your SPF, DKIM, and DMARC records are correctly set up and aligned.
Common pitfalls
Continuing to send to old, unengaged or deprecated rr.com addresses.
Ignoring specific bounce codes from RoadRunner, such as AUP#In-1310.
Sending high volumes to RoadRunner domains without prior history or good engagement.
Lack of proper email authentication (SPF, DKIM, DMARC) or misconfigurations.
Expert tips
Always keep an eye on your email engagement metrics, as ISPs like RoadRunner factor this into their filtering decisions.
For specific blockages, sometimes the only path to resolution is through direct communication with the ISP or the filtering service they employ.
Consider reducing your sending frequency or volume to RoadRunner domains if you consistently see high deferral rates.
Implement a double opt-in process for all new subscribers to ensure high quality and reduce spam complaints.
Marketer view
Marketer from Email Geeks says they consistently encounter issues with RoadRunner, even when adhering to good sending practices.
2020-07-09 - Email Geeks
Marketer view
Marketer from Email Geeks says they have struggled with cable-based email providers and the absence of clear postmaster contacts.
