Summary
Email throttling with Spectrum/TWC involves rate limiting, often indicated by AUP#13XX codes from Cloudmark (Charter Communications). Diagnosing requires gathering data like timestamps and error messages, particularly noting 'exceeded maximum connection limit'. Key strategies include contacting Cloudmark, monitoring bounce messages, gradually warming up IPs, segmenting lists, distributing emails across IPs, and potentially using throttling software. Improving sender reputation via list hygiene, SPF/DKIM/DMARC, and easy unsubscribe options is crucial, and understanding the mail system configuration is essential. Even Spectrum/TWC's own emails may face deliverability issues.
Key findings
- Cloudmark Throttling: Spectrum/TWC uses Cloudmark for rate limiting, indicated by AUP#13XX codes.
- Internal Issues Exist: Spectrum/TWC also experiences deliverability challenges internally.
- Error Analysis: Error messages provide insight into the cause of throttling.
- Data-Driven Diagnosis: Diagnosing requires gathering timestamps, IPs, and specific error messages.
- Rate Limiting Standard Practice: SMTP servers and ESPs use rate limiting to manage load and prevent abuse.
- Reputation Impact: Poor list hygiene and sending practices negatively impact reputation, increasing the likelihood of throttling.
- IP Warmup Importance: Warming up IP addresses is essential to prevent triggering throttling.
- Segmentation Benefits: List segmentation reduces the perceived volume of emails.
Key considerations
- Contact Cloudmark: Reach out to Cloudmark for direct assistance with throttling issues.
- Monitor Bounces: Continuously monitor bounce messages for specific error codes.
- Gather Data: Collect timestamps, IPs, and error messages for detailed analysis.
- Improve List Hygiene: Focus on building a clean email list and removing inactive or invalid addresses.
- Authenticate Email: Implement SPF, DKIM, and DMARC to improve sender authentication.
- Gradual IP Warmup: Implement a gradual IP warm-up process with smaller sending volumes.
- Segment Email List: Segment email lists and stagger sends to reduce the perceived volume.
- Review System Configuration: Understand mail sending system configuration to identify bottlenecks.
What email marketers say
12 marketer opinions
Email throttling with Spectrum/TWC often involves rate limiting, indicated by AUP#13XX codes, as Charter Communications (Cloudmark) imposes restrictions. Troubleshooting involves contacting Cloudmark, monitoring bounce messages for error codes, and adjusting sending volume. Strategies include warming up IP addresses gradually, segmenting email lists, spreading email over multiple IP addresses, and using throttling software. Improving sender reputation through clean lists, authentication (SPF, DKIM, DMARC), and easy unsubscribe options also helps. Internal challenges within Spectrum/TWC may also contribute to deliverability issues.
Key opinions
- Rate Limiting: Spectrum/TWC uses rate limiting (AUP#13XX codes) implemented by Cloudmark, indicating a desire for slower email delivery rather than direct reputation blocks.
- Internal Issues: Even Spectrum/TWC's own emails experience deliverability problems to their clients.
- Bounce Monitoring: Monitoring bounce messages for specific error codes helps identify the cause of throttling and allows for adjustments in sending practices.
- IP Warm-up: Gradually warming up IP addresses is crucial to avoid triggering throttling mechanisms by establishing a sending reputation over time.
- List Segmentation: Segmenting email lists and staggering sends helps reduce the perceived volume of emails, mitigating throttling triggers.
- Sender Reputation: Maintaining a clean email list, authenticating email with SPF, DKIM, and DMARC, and providing easy unsubscribe options are vital for improving sender reputation.
Key considerations
- Contact Cloudmark: Reach out to Cloudmark for troubleshooting assistance, as they manage Charter Communications' email security.
- Throttling Software: Consider using real-time email throttling software to analyze delivery and adjust sending parameters.
- Multiple IPs: Distribute email traffic across multiple IP addresses to avoid overwhelming recipient servers.
- Adjust Sending Volume: Reduce sending volume to spectrum/TWC and watch to see if the throttling reduces.
- Engagement Metrics: Monitor engagement metrics, such as opens and clicks, to assess the impact of sending adjustments and further refine strategies.
Marketer view
Email marketer from Reddit suggests throttling can be due to the recipient server limiting the number of connections or emails it accepts from a particular IP address within a given time frame. They advise monitoring the specific error codes returned in bounce messages to identify the cause and adjust sending practices accordingly.
11 May 2025 - Reddit
Marketer view
Email marketer from ExpertSender recommends configuring SPF/DKIM/DMARC records, implement a double opt-in sign-up process, and provide clear unsubscribe links in your emails. These measures improve sender reputation and reduce the likelihood of being throttled.
21 Apr 2025 - ExpertSender
What the experts say
3 expert opinions
Email throttling is often related to underlying sender reputation issues or connection limits, requiring careful diagnosis and data gathering. Analyzing error messages for specifics like 'exceeded maximum connection limit' and understanding the type of throttle imposed are vital. Poor list hygiene or questionable sending practices can lead to throttling; improving sender reputation with best practices is often necessary.
Key opinions
- Detailed Data Needed: Diagnosing throttling necessitates detailed data: timestamps, target IPs, error messages.
- Error Messages: Error messages provide key insights (e.g., 'exceeded maximum connection limit').
- Reputation Link: Throttling is frequently a symptom of underlying sender reputation issues.
- Configuration Matters: Understanding mail system configuration aids in resolving throttling.
Key considerations
- Gather Data: Collect timestamps, target IPs, and error messages to understand the issue better.
- Analyze Error Codes: Carefully examine the error codes returned to understand the cause.
- Improve Reputation: Focus on improving list hygiene and implementing best sending practices.
- Review Configuration: Review your mail sending system's configuration to identify potential bottlenecks.
Expert view
Expert from Word to the Wise explains that diagnosing connection throttling issues requires gathering detailed data, including timestamps, target IP addresses, and error messages. He also explains that understanding how your mail-sending system is configured is important, and knowing the specific type of throttle being imposed can help you resolve it.
28 May 2023 - Word to the Wise
Expert view
Expert from Word to the Wise explains that when experiencing throttling, it is important to look at the error message returned. These error messages will usually include information relating to why you have been throttled, such as "exceeded maximum connection limit".
3 Jun 2025 - Word to the Wise
What the documentation says
5 technical articles
SMTP servers and email service providers (ESPs) like PowerMTA, Microsoft Exchange Online, Google Workspace, and Amazon SES implement rate limiting and sending limits to manage server load, prevent abuse, and maintain system health. These limits are based on factors like sender IP, domain, message content, recipient rate, and message size. Resolving throttling requires adhering to sending guidelines (SPF, DKIM, DMARC, unsubscribe options), monitoring bounce messages for error codes, configuring concurrency and retry settings, and staying within defined limits.
Key findings
- Rate Limiting Standard: SMTP servers use rate limiting based on IP, domain, and message content for load management.
- Configurable Throttling: Tools like PowerMTA allow administrators to configure concurrency and retry settings.
- Service Limits: ESPs such as Exchange Online, Google Workspace, and Amazon SES impose sending limits.
- Abuse Prevention: Sending limits and rate limiting are in place to protect against spam and abuse.
- Bounce Monitoring: Monitoring bounce messages for error codes is crucial for understanding the cause of throttling.
Key considerations
- Adhere to Guidelines: Adhere to bulk sending guidelines provided by ISPs and ESPs (SPF, DKIM, DMARC).
- Monitor Error Codes: Pay close attention to bounce messages and interpret the specific error codes.
- Configure Retries: Adjust concurrency and retry settings to optimize email delivery.
- Stay within Limits: Ensure that sending practices remain within the defined sending limits of the service.
Technical article
Documentation from Microsoft Learn states that Exchange Online implements sending limits to protect against spam and maintain system health. These limits include recipient rate limits, sending limits, and message size restrictions. Exceeding these limits can result in temporary or permanent sending restrictions.
13 May 2023 - Microsoft Learn
Technical article
Documentation from Google Workspace Admin Help advises bulk email senders to adhere to their bulk sending guidelines, which include authenticating email with SPF, DKIM, and DMARC, maintaining low spam complaint rates, and providing easy unsubscribe options. They also recommend monitoring bounce messages for specific error codes.
18 Apr 2023 - Google Workspace Admin Help
How do I contact the AT&T postmaster and what domains are associated with their email filtering?
How do I contact the Yahoo postmaster for deliverability issues during IP warm-up?
How do I resolve blocking issues with Charter/Spectrum?
How do I resolve email blocking issues with Apple servers and postmasters?
How to contact Spectrum/Charter postmaster for email delivery issues?
How to resolve email throttling issues with Charter.net when sending high volumes of email?
