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How to improve email deliverability to Sina.com and Sina.cn in China and handle rate limits?

Summary

Achieving strong email deliverability to Sina.com and Sina.cn in China presents unique challenges due to stringent government regulations, ISP-specific filters, and a preference for transactional over bulk email. Senders must adopt an extremely cautious and adaptive approach to overcome these hurdles. Key strategies involve significantly reducing sending volume and implementing dynamic throttling to navigate strict rate limits, alongside employing dedicated IP infrastructure, ideally located within China or APNIC ranges. Content must be meticulously crafted in Simplified Chinese, be mobile-first, and strictly avoid sensitive or politically charged topics. Moreover, maintaining an impeccably clean, permission-based email list, ensuring robust sender authentication, and continuously monitoring deliverability metrics are critical to building and preserving a positive sender reputation with these highly sensitive ISPs.

Key findings

  • Sina's Difficulty: Sina.com and Sina.cn are exceptionally challenging email providers for deliverability due to stringent filtering, lack of transparency, and sensitivity to sending patterns.
  • Rate Limiting: Chinese ISPs, including Sina, primarily use throttling mechanisms rather than strict daily sending limits, meaning sending too quickly will lead to temporary rejections and deferrals.
  • Infrastructure Optimization: Email infrastructure in China is largely optimized for transactional emails, not bulk marketing campaigns, which are often conducted through local applications like WeChat.
  • IP Filtering: Western IP ranges often face automatic filtering, and Chinese ISPs frequently block emails based on the sending domain and IP address, impacting deliverability even for legitimate communications.
  • User Sensitivity: Chinese ISPs are highly sensitive to user complaints, making engaged lists and highly relevant content paramount to maintaining sender reputation.

Key considerations

  • Throttled Sending: Implement extremely slow sending rates to Sina.com and Sina.cn, potentially as low as 8 messages per minute or less than 500 per hour, adjusting dynamically based on deferral messages and applying exponential backoff for retries. Send emails in smaller batches spread throughout the day rather than large bursts.
  • Dedicated Infrastructure: Utilize dedicated IP addresses, ideally those within Chinese or APNIC ranges, or use an Email Service Provider with strong existing connections and specialized infrastructure for China deliverability. Segment your Chinese recipients and use separate sending IPs and domains for this audience.
  • Content Compliance: Ensure all email content is in Simplified Chinese, is mobile-first, and avoids politically sensitive, pornographic, or controversial topics. Avoid common URL shorteners and host images on Chinese CDNs to ensure quick loading. The content should be highly relevant and expected by the recipient to minimize complaints.
  • Sender Reputation & List Hygiene: Maintain an extremely clean, permission-based mailing list with explicit consent for all recipients. Regularly clean inactive or bouncing addresses. Ensure robust sender authentication (SPF, DKIM, DMARC). Focus on fostering high engagement to keep complaint rates very low, as Chinese ISPs are highly sensitive to user feedback.
  • Continuous Monitoring: Implement a continuous feedback loop and adjustment strategy. Monitor bounce codes, IP reputation, and sender feedback loops closely, using adaptive sending algorithms that automatically slow down and gradually resume sending when transient errors or rate limits are encountered.

What email marketers say

12 marketer opinions

Further insights into delivering emails to Sina.com and Sina.cn underscore that success hinges on a deep understanding of their stringent rate limits and the unique characteristics of China's email ecosystem. It's evident that the infrastructure prioritizes transactional communications over large-scale marketing, often better suited for local platforms like WeChat. Therefore, senders must apply extremely precise volume control, deploy localized sending infrastructure, and meticulously tailor content for the Chinese audience. Crucially, maintaining an impeccable sender reputation through strict adherence to consent, rigorous list hygiene, and continuous adaptive monitoring is essential to navigate Sina's highly sensitive filtering and throttling mechanisms.

Key opinions

  • Extreme Throttling Requirements: Sina.com and Sina.cn enforce highly aggressive rate limits, often demanding extremely low sending rates, potentially 8 messages per minute or less than 500 per hour, highlighting the need for gradual and adaptive sending.
  • Specialized Infrastructure: Effective delivery often requires dedicated sending IPs and domains within Chinese or APNIC IP ranges, or partnering with an ESP boasting strong local connections and optimized infrastructure for China, as Western IPs frequently encounter automatic filtering.
  • Market Misalignment for Bulk: China's email infrastructure is primarily built for transactional messages, not extensive marketing campaigns, which are more commonly executed via local applications like WeChat. Attempting bulk email sends to China often indicates a misunderstanding of local market dynamics.
  • Foundational DNS & Reputation: Strong SPF, DKIM, and DMARC policies are fundamental, alongside meticulous list hygiene and minimal complaint rates, to establish and preserve a positive sender reputation with China's sensitive ISPs.
  • Content and Mobile Imperatives: Emails must be mobile-first, utilize Simplified Chinese, and rigorously avoid politically sensitive or culturally inappropriate content to successfully pass through stringent content filters.

Key considerations

  • Implement Adaptive Throttling: Adopt sophisticated, adaptive rate-limiting strategies like exponential backoff for retries, gradually increasing send volume for new IPs, and intelligently increasing delay times after failed attempts. Distribute sends in smaller batches throughout the day rather than large bursts to avoid overwhelming recipient servers.
  • Leverage Localized ESPs and IPs: Prioritize using Email Service Providers with established relationships and specialized infrastructure in China, including IPs within local ranges. Segment Chinese recipients to ensure their emails are sent from dedicated IPs and domains optimized for the region, as Western IPs often face automatic filtering.
  • Optimize Content for Chinese Audience: Ensure all email content is in Simplified Chinese, is designed for mobile-first viewing, and loads quickly by hosting images on servers accessible within China. Crucially, remove any potentially sensitive or misinterpreted content to comply with strict filtering rules.
  • Uphold Strict List Hygiene and Consent: Mandate explicit consent for all recipients and provide clear, easily accessible unsubscribe options. Regularly clean lists of inactive or bouncing addresses. High complaint rates are detrimental, so focus on highly engaged lists and relevant content to maintain a positive sender reputation.
  • Strengthen Authentication (SPF, DKIM, DMARC): Ensure all DNS records, especially SPF, DKIM, and DMARC, are correctly implemented and robust. These are non-negotiable for establishing sender trust and improving deliverability through China's complex landscape.
  • Employ Continuous Feedback Loop Monitoring: Maintain an ongoing process of monitoring bounce codes, IP reputation, and feedback loops. Be ready to adjust sending patterns, pause sends, and refine strategies based on real-time deliverability performance and ISP responses.

Marketer view

Marketer from Email Geeks explains that delivering to China can be challenging, suggesting that sending on Chinese or APNIC range IPs might improve performance and that getting added to a whitelist may also be an option.

18 Mar 2025 - Email Geeks

Marketer view

Marketer from Email Geeks explains that Sina's deferral message typically means stopping sending from the current IP and reducing volume, suggesting throttling sends down to a low level, possibly less than 500 per hour.

11 Jan 2023 - Email Geeks

What the experts say

2 expert opinions

Improving email deliverability to challenging Chinese providers like Sina.com and Sina.cn requires continuous adaptation from senders, primarily due to the inherent lack of transparency from Chinese ISPs regarding their complex filtering criteria. Unlike fixed daily limits, these providers typically employ throttling mechanisms, meaning sending too quickly will lead to temporary rejections. Therefore, senders must prioritize a consistent, gradual sending pace, rigorous list hygiene, and proactive bounce rate management to build and sustain a positive sender reputation and avoid frequent blocking of sending domains and IP addresses.

Key opinions

  • ISP Transparency Issues: Chinese ISPs, including Sina, are notably opaque about their filtering criteria, making it difficult for senders to understand specific blocks. They frequently block emails based on the sending domain and IP address, impacting legitimate communications.
  • Throttling, Not Fixed Limits: Instead of strict daily sending limits, Chinese internet service providers predominantly utilize throttling. Sending a large volume of emails too quickly will result in temporary rejections and deferrals.
  • Adaptation and Hygiene: Successful deliverability necessitates senders consistently adapting their sending habits, maintaining extremely clean mailing lists, and actively managing bounce rates to circumvent frequent blocking and improve performance.
  • Gradual Sending Benefits: Adopting a consistent and more gradual sending pace is crucial for building and maintaining a positive sender reputation with Chinese ISPs, effectively mitigating throttling and improving overall deliverability.

Key considerations

  • Implement Gradual Sending: Adopt a consistent and significantly more gradual sending pace when targeting Sina.com and Sina.cn. This approach helps to build and maintain a positive sender reputation, reducing temporary rejections caused by throttling.
  • Prioritize List Cleanliness: Maintain an exceptionally clean mailing list by diligently removing unengaged or bouncing addresses. Proactive list hygiene is vital for reducing bounce rates and minimizing the risk of domain and IP blocks from sensitive Chinese ISPs.
  • Continuous Adaptation: Given the lack of transparency from Chinese ISPs regarding their filtering, senders must be prepared to continuously adapt their sending habits and strategies to navigate evolving deliverability challenges.

Expert view

Expert from Word to the Wise shares that email deliverability to China, including major providers like Sina, presents significant challenges due to the lack of transparency from Chinese ISPs regarding their filtering criteria. To improve deliverability, senders must consistently adapt their sending habits, maintain extremely clean mailing lists, and actively manage bounce rates. Chinese ISPs frequently block emails based on the sending domain and IP address, which often results in poor deliverability even for legitimate communications.

10 Dec 2022 - Word to the Wise

Expert view

Expert from Word to the Wise explains that internet service providers (ISPs) typically utilize throttling mechanisms instead of strict daily sending rate limits. Sending a large volume of emails too quickly can lead to temporary rejections. To enhance deliverability and mitigate throttling, especially when dealing with challenging ISPs such as those in China, senders should adopt a consistent and more gradual sending pace. This approach helps to build and maintain a positive sender reputation with the ISPs.

7 Aug 2023 - Word to the Wise

What the documentation says

5 technical articles

The complexity of email deliverability to Chinese providers such as Sina.com and Sina.cn is further amplified by their unique operational environments. Success hinges on a sender's ability to maintain an impeccable IP reputation, adhere strictly to content compliance, and implement highly adaptive sending strategies to navigate dynamic rate limits. It is crucial to employ dedicated IP infrastructure, tailor content meticulously for the Chinese audience, and prioritize strong sender authentication and rigorous list hygiene to withstand their stringent filtering mechanisms.

Key findings

  • Content Filtering Intensity: Emails to Sina.com and Sina.cn face heightened scrutiny, requiring meticulous content that avoids spam triggers, banned keywords, and common URL shorteners, with a strong preference for Simplified Chinese.
  • Dedicated IP Strategy: Utilizing separate, dedicated IP addresses or pools for China traffic is widely recommended by ESPs to isolate sender reputation and enhance deliverability performance.
  • Dynamic Throttling: Managing rate limits requires implementing dynamic or adaptive sending algorithms that automatically adjust sending speed based on ISP responses, such as bounce codes or transient errors.
  • Permission-Based Lists & Engagement: Maintaining a strictly permission-based mailing list with high recipient engagement and a very low complaint rate is crucial, as Chinese ISPs are highly sensitive to user feedback and enforce strict anti-spam laws.
  • Constant Evolving Landscape: Deliverability to Chinese providers can be unpredictable due to frequent and often unannounced changes in filtering rules and regulations.

Key considerations

  • Meticulous Content Optimization: Craft email content entirely in Simplified Chinese, ensuring it is highly relevant and expected by recipients. Rigorously avoid spam trigger words, banned keywords, common URL shorteners, politically sensitive, or pornographic material. Host images on Chinese CDNs to ensure fast loading and accessibility.
  • Strategic IP Management: Utilize separate, dedicated IP addresses for China traffic to isolate and protect your sender reputation. If using new IPs, implement a slow and careful IP warm-up process to build trust with Chinese ISPs like Sina.
  • Adaptive Sending Rate Algorithms: Implement sophisticated adaptive sending algorithms that dynamically adjust sending speed based on real-time ISP responses, such as bounce codes or rate limit messages, slowing down immediately upon detection and gradually resuming.
  • Rigorous List Hygiene and Consent: Maintain an impeccably clean, permission-based mailing list with clear consent and easy unsubscribe options. Focus on fostering high engagement to achieve and maintain extremely low complaint and bounce rates, which are critical for deliverability in China.
  • Robust Sender Authentication: Ensure that SPF, DKIM, and DMARC records are correctly configured and enforced to establish and maintain sender trust, which is a foundational requirement for all major email providers, including Sina.

Technical article

Documentation from SendGrid explains that sending email to China, including providers like Sina.com, requires careful attention to content, IP reputation, and local regulations. They emphasize maintaining a clean list, avoiding spam trigger words, and ensuring proper sender authentication (SPF, DKIM). It's crucial to understand that content often undergoes more stringent filtering, and a higher bounce rate can impact reputation. They also advise against using link shorteners or common URL shorteners as they are often blocked.

31 Oct 2022 - SendGrid Blog

Technical article

Documentation from Mailgun highlights that email deliverability in China is challenging due to strict government regulations and ISP-specific filters. For providers like Sina.com, it's essential to use dedicated IPs, ensure all content is in Simplified Chinese, and avoid banned keywords. They advise on warming up IPs slowly, maintaining a low complaint rate, and specifically mentioning that images should be hosted on Chinese CDNs if possible to avoid loading issues. Handling rate limits involves monitoring bounce codes and adjusting sending speed accordingly.

20 Apr 2022 - Mailgun Blog

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