Summary
Email throttling from Spectrum, formerly Time Warner Cable (TWC) and Roadrunner, is a common deliverability challenge. It typically manifests as delayed email deliveries, often accompanied by specific bounce codes like AUP#In-1380 or server temporarily unavailable. This throttling is often due to internal rate-limiting policies rather than direct reputation blocks, meaning Spectrum intentionally slows down the incoming mail flow to manage server load or enforce sending best practices, even for senders with a good reputation. Resolving these issues requires a strategic approach to sending practices and sometimes direct communication.
Key findings
- Rate limits: Spectrum/TWC's throttling often stems from internal rate-limiting rather than specific reputation issues, even for legitimate mail. This means they are designed to slow down email receipt, not block it entirely.
- Specific error codes: The error code AUP#In-1380 is a common indicator of these rate limits, signifying a temporary server unavailability due to acceptable use policy enforcement.
- Persistent delays: Throttling can lead to significant delays in email delivery, sometimes hours or even days, which is particularly problematic for time-sensitive communications.
- Cloudmark integration: Charter Communications (Spectrum's parent company) utilizes Cloudmark for spam and threat protection, which can influence how emails are handled and subjected to throttling or blocklisting.
- Internal challenges: Even internal business units within Spectrum can experience delivery challenges with their own email campaigns, highlighting the strictness of their mail policies.
Key considerations
- Implement back-off rules: Employing robust custom back-off rules in your sending system can help manage the throttling by retrying emails at increasing intervals, preventing hard bounces while respecting the recipient server's limits. Learn more about how to prevent email throttling from various email clients.
- Gradual sending: Adopt a slower, more gradual sending pace to Spectrum/TWC domains. This aligns with their preference for mail to arrive very very slow, reducing the likelihood of hitting rate limits.
- Monitor delivery metrics: Continuously monitor your email delivery rates and bounce codes specifically for Spectrum/TWC. Tools can help identify if you're hitting rate limits consistently.
- Direct engagement: Attempting to establish direct communication with Spectrum's postmaster team or Cloudmark support can sometimes yield specific guidance or whitelisting, especially for critical, time-sensitive mailings. You can often find contact information on their postmaster sites (for example, see Cloudmark's contact page). For more on specific issues, consider troubleshooting email delivery issues with Charter/TWC (Spectrum/Roadrunner).
What email marketers say
Email marketers frequently encounter throttling issues with Spectrum/TWC, often finding that even strong sender reputations don't prevent these delays. The consensus among marketers is that these are primarily rate-limiting challenges. Many express frustration over the significant delays for crucial communications, and some even highlight the irony of Spectrum's own business units facing similar deliverability hurdles.
Key opinions
- Reputation vs. Rate limits: A common belief is that throttling is more about rate limits enforced by ISPs like Spectrum, rather than a reflection of poor sender reputation. This is especially true when error codes like AUP#13XX are observed.
- Slow delivery preference: Many marketers note that Spectrum (and related networks like Roadrunner) appear to prefer a very slow and gradual delivery of emails.
- Impact on time-sensitive mail: Delays can severely impact the effectiveness of urgent or time-critical email campaigns, leading to frustration for senders.
- Cloudmark's role: The involvement of third-party security providers like Cloudmark, used by Charter Communications, is seen as a key factor in email filtering and throttling decisions.
- Internal struggles: A surprising opinion among marketers is that even Spectrum's own internal email delivery can suffer from similar throttling, illustrating the pervasive nature of these challenges.
Key considerations
- Adopt custom back-off rules: Marketers emphasize the necessity of finely tuned back-off rules to manage temporary deferrals effectively, allowing emails to eventually get through.
- Patience and persistence: Given Spectrum's preference for slow delivery, marketers must be prepared for longer delivery times and maintain consistent sending practices over time.
- Identify postmaster contacts: Seeking direct contacts at Spectrum/TWC or Cloudmark can be beneficial for escalating urgent issues or understanding specific policies. For example, knowing where to find Roadrunner and Spectrum postmaster site information is crucial.
- Ongoing monitoring: Continuous monitoring of email logs and bounce rates specifically for Spectrum domains is advised to track the impact of throttling and adjust sending strategies accordingly.
- Sender reputation management: While throttling may not be directly reputation-based, maintaining a stellar sender reputation (e.g., low spam complaints, valid lists) remains foundational for overall deliverability. This also applies to issues like slow email delivery to Gmail.
Marketer view
Marketer from Email Geeks notes encountering "server temporarily unavailable AUP#In-1380" errors when trying to send important COVID-related emails. The persistent nature of these errors, despite custom back-off rules, indicates a significant challenge in achieving timely delivery.
Marketer view
Marketer from Email Geeks clarifies that the AUP#13XX codes, often seen with Spectrum, are typically rate-limits from Cloudmark (formerly misidentified as Comcast). They state that these codes signify Spectrum's desire for emails to arrive very slowly, irrespective of sender reputation.
What the experts say
Email deliverability experts highlight that throttling by major ISPs like Spectrum/TWC is a nuanced issue, often distinct from outright blacklisting. They emphasize that while reputation is always key, these specific AUP (Acceptable Use Policy) related throttling events indicate intentional rate-limiting rather than a punitive block. Experts typically recommend sophisticated sending practices and direct engagement where possible, underscoring that even the best senders can face these challenges.
Key opinions
- Throttling vs. Blocking: Experts differentiate between throttling (slow delivery) and hard blocking (rejection), noting that Spectrum's AUP codes typically point to the former, which is managed differently than a blacklist removal.
- Sender behavior: Aggressive sending patterns, even from good IPs, can trigger throttling. ISPs prefer a consistent, slower flow of mail.
- Policy-driven: These throttles are often based on Spectrum's internal Acceptable Use Policies and capacity management, not necessarily direct spam complaints against a specific sender.
- Third-party filters: The use of services like Cloudmark by Spectrum means that their filtering decisions are influenced by a comprehensive threat intelligence network.
Key considerations
- Optimize sending rates: Adapt your sending infrastructure to dynamically adjust rates to Spectrum's domains, gradually increasing volume and backing off upon deferrals.
- Monitor specific bounces: Pay close attention to 4xx temporary failures and codes like AUP#In-1380 to understand the precise nature of the throttling. This is similar to resolving Yahoo TS-04 email delivery errors.
- Postmaster communication: While difficult, attempting to reach out to Spectrum's postmaster team or Cloudmark support can provide insights or aid in specific cases, especially for high-volume, legitimate senders.
- Maintain sender reputation: Even if throttling isn't reputation-based, a strong sender reputation built on good list hygiene, low complaints, and proper authentication (SPF, DKIM, DMARC) is essential for long-term inbox placement and avoiding other forms of blocklisting. This is key to boosting email deliverability rates.
Expert view
Expert from Email Geeks suggests that while email reputation is important, specific throttling issues like those from Spectrum often indicate internal rate-limiting policies rather than a direct block due to poor standing. This means senders need to adjust their sending speed, not necessarily fix a reputation problem.
Expert view
Expert from Email Geeks advises that aggressive sending, even with legitimate mail, can trigger temporary deferrals. ISPs like Spectrum prefer a slower, more consistent flow of emails to maintain network stability and prevent abuse.
What the documentation says
Official documentation and technical reports often detail the mechanisms behind email throttling and blocklisting implemented by ISPs and security vendors. These documents clarify that temporary errors like 4xx codes are typically soft rejections, allowing for retries, and are distinct from permanent 5xx errors. They also explain the role of Acceptable Use Policies in governing mail flow and the function of reputation systems in determining delivery speed and acceptance.
Key findings
- Temporary error codes (4xx): These codes, such as 421 or 451 (like AUP#In-1380), indicate that the recipient server is temporarily unable to accept mail, requiring the sender to retry later.
- Rate-limiting enforcement: ISPs implement rate limits to protect their infrastructure from overload and malicious activity. These limits dictate how many emails a particular sender can send within a given timeframe.
- Acceptable use policies (AUPs): AUPs define the rules and conditions for using an ISP's email services. Violations can lead to throttling, deferrals, or even permanent blocks. AUP#In-1380 suggests a policy violation related to inbound mail processing.
- Reputation system integration: While throttling can be distinct from reputation-based blocking, an ISP's internal reputation system (which may include data from services like Cloudmark) often influences the severity and duration of throttling. This means a positive reputation can lead to faster resolution of throttling issues.
Key considerations
- Adherence to RFCs: Ensure your sending practices align with standard email protocols (RFCs) to minimize unexpected deferrals. Understanding what RFC 5322 says versus what actually works can be beneficial.
- Implementation of retry logic: Email servers should be configured with intelligent retry mechanisms for 4xx errors, allowing for successful delivery once the throttling eases. This is critical for avoiding email backscatter, an issue that can arise from improper handling of bounces and deferrals.
- Understanding ISP-specific policies: Reviewing postmaster guidelines or AUPs published by Spectrum (or its parent Charter Communications) can provide specific details on their preferred sending volumes and acceptable behavior. One such resource is a help article regarding Time Warner from Returnpath.
- Authentication standards: Ensuring proper SPF, DKIM, and DMARC records are in place helps ISPs verify sender legitimacy, reducing the likelihood of throttling or blocklisting due to perceived spoofing or phishing attempts.
Technical article
Documentation from Returnpath explains that temporary deferrals, often indicated by specific SMTP error codes like 421 or 451, signal that an email server is temporarily overloaded or enforcing policy, but will likely accept the email upon retry. This is distinct from permanent rejections.
Technical article
RFC 5321 (SMTP) specifies that transient negative completion replies (4xx codes) mean the command did not succeed, but the error condition is temporary, and the client should try again. This forms the basis for email throttling mechanisms.
Related resources
10 resources
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