How to troubleshoot email sending issues to Cox, Charter, and Optonline domains?

Key findings

• Large sends impact deliverability: High volume email campaigns can lead to on-and-off deliverability issues, especially for Cox.net, Charter.net (Spectrum Communications), and Optonline.net.
• Inconsistent sending cadence: A lack of regular large sends can harm sender reputation and require a re-warming process.
• Temporary suspensions: Receiving 550.5.1.0 bounces indicates the subscriber's email address is temporarily suspended for 24 hours.
• Geographic impact: Deliverability can be particularly challenging in states with a high concentration of subscribers from these problematic domains.
• Warming up: Targeted, smaller send batches with throttling are effective for rebuilding sending reputation to specific domains.

Key considerations

• Cadence is key: Maintain a consistent and regular sending cadence to ensure steady deliverability.
• Segment your audience: For specific domains like Charter/TWC (Spectrum/Roadrunner), consider breaking down your sends into smaller, more manageable batches to avoid overwhelming ISP servers.
• Throttle intelligently: Implement throttling, such as sending 500 emails every 30 minutes to an hour per domain, to manage send volume and avoid triggering ISP rate limits.
• Monitor bounce codes: Understand and track specific bounce codes like 550.5.1.0 to differentiate between temporary and permanent issues. You can find more information about SMTP port issues on HP community forums.
• Patience is a virtue: Re-warming a neglected sender reputation takes time and consistent effort. There is no quick fix for a damaged reputation, and gradually increasing volumes is crucial.

Key opinions

• Bounce code interpretation: The 550.5.1.0 bounce code suggests a temporary subscriber suspension, not necessarily a direct reputation issue with the sender.
• ISP consolidation: Charter.net is part of Spectrum Communications and includes RoadRunner domains, indicating a broader network of associated domains that might experience similar issues.
• Warming strategies: There's debate on whether to follow a rigid daily email warmup schedule or to test small batches from a given list.

Key considerations

• Understanding bounce messages: It's critical to interpret bounce messages accurately to determine if the issue is sender-related or subscriber-specific. For specific errors, refer to our guide on common email delivery issues with Cox.
• Targeted re-engagement: If a specific segment of your list has been dormant, re-engaging them with small, carefully throttled sends is advised. This can help with issues like Optimum/Optonline/Altice/Synchronoss blockages.
• ISP specific considerations: Recognizing that ISPs have their own configurations and practices is essential for effective troubleshooting.

Key opinions

• Subscriber-specific issues: The suspension of a subscriber's email address by the ISP may not be a direct reflection of the sender's reputation but rather an ISP-level action on the recipient's side.
• Data analysis is key: Providing IP details and analyzing traffic data can offer deeper insights into deliverability problems that might not be immediately apparent.
• Beyond sender reputation: Not all sending failures are due to a bad sender reputation; some can be caused by ISP policies or subscriber account states.

Key considerations

• Differentiating bounce types: Accurately identifying whether a bounce is due to a temporary subscriber suspension or a general sending block is crucial. For more details on bounce issues, see our guide on Charter/Spectrum concurrent connection bounces.
• Leverage expert offers: Take advantage of offers from experts to analyze IP traffic and identify underlying issues.
• Holistic view: Consider all potential factors, including ISP throttling and internal practices, when troubleshooting. Our article on why your emails fail offers broader insights.

Key findings

• SMTP port usage: SMTP typically uses TCP port 25 or 2525. ISPs may block port 25 to reduce spam, causing sending problems for senders not using alternative ports.
• ISP-specific addresses: Each ISP (Cox, Charter, Optonline) has specific SMTP server addresses and configurations that must be correctly used by senders.
• Troubleshooting methodologies: Standard troubleshooting often involves checking SMTP port status and verifying server settings.

Key considerations

• Port 25 blocking: Be aware that many ISPs (including potentially Cox, Charter, and Optonline) block outbound port 25 for residential and even some business connections to combat spam. Consider using alternative ports like 587 (submission) or 465 (SMTPS).
• AUP compliance: Adhering to the Acceptable Use Policies of Cox, Charter, and Optonline is critical to avoid blocks. Bounce codes like AUP#I-1010 for Charter indicate AUP violations. Learn more about Cox.net AUP#CXCNCT rejections.
• Server address verification: Ensure you are using the correct and up-to-date SMTP server addresses for these ISPs. Improper server configuration is a common cause of sending failures. For general troubleshooting, refer to resources like Scarlett's Web's list of ISP addresses.
• Throttling mechanisms: ISPs like Charter.net implement throttling to manage incoming email volume. Senders should understand these limits and adjust sending rates accordingly to avoid temporary blocks. Read about Charter.net throttling for high volumes.