What are the best practices for sending email to Polish providers like Interia to avoid throttling?

Key findings

• Aggressive throttling: Polish providers, notably Interia, frequently apply heavy throttling, causing emails to expire in queues rather than bounce immediately.
• Widespread impact: This throttling appears to be a general issue across shared IP environments, not confined to specific problematic senders.
• Limited support: Direct support from these mailbox providers for deliverability issues is often unresponsive.
• Authentication importance: Proper email authentication (SPF, DKIM, DMARC) and domain alignment are vital, especially for shared IP sending, as European providers typically favor fully authenticated mail.
• Volume sensitivity: Even relatively low volumes, such as 7,780 emails over four days, can trigger extensive queue times and throttling.

Key considerations

• Gradual sending: Space out email sends and adopt a gradual warming approach, starting with small volumes and slowly increasing, as outlined in our guide on staggering email sends.
• Robust authentication: Ensure your domain is properly authenticated with SPF, DKIM, and DMARC. This is a foundational best practice for increasing email deliverability.
• Monitor logs: Pay close attention to send logs for throttling messages, even if no hard bounces occur. These indicate rate limits imposed by the provider.
• List hygiene: Maintain a clean email list to minimize bounces and avoid spam traps. Our guide on email deliverability best practices offers more insights.

Key opinions

• General throttling: Polish providers exhibit a widespread tendency to throttle, rather than block, mail, often until the delivery time expires.
• Unresponsive support: Efforts to contact support or request delistings generally result in automated responses and no change in deliverability.
• Pay-to-play model: There's a strong perception that Polish providers, like Interia, may have a "pay-to-play" model or certification programs (such as Trusted Sender) to gain inbox preference.
• Volume misjudgment: Volumes that seem perfectly acceptable to marketers (e.g., ~7,780 emails over four days to a single domain) can still lead to severe throttling.
• Authentication uncertainty: While authentication is suspected as a factor, providers often remain unclear about its specific role in throttling.

Key considerations

• Understand rate limits: Polish providers may have highly sensitive or undisclosed sending rate limits, even for what seems like low volume for shared IPs. Learn more about handling email sending rate limits.
• Test different IPs: If using shared IPs, testing different ranges with smaller volumes might reveal if specific IP reputation issues are contributing to the throttling.
• Focus on reputation: Prioritize overall sender reputation, even if specific reasons for throttling are unclear. This includes managing bounces and complaints effectively, as advised by EmailTooltester.com.
• Consider domain alignment: Implement domain alignment, such as CNAMES for return path domains, as this is often preferred by European providers and can aid deliverability.

Key opinions

• Aggressive european throttling: European providers generally throttle more aggressively than their counterparts in other regions, making volume management critical.
• Authentication preference: There's a strong preference for fully authenticated mail and proper domain alignment (e.g., CNAMEs for return paths) among providers like GMX.
• Volume guidelines: A common recommendation for Polish providers is to start sending as low as 1,000 messages per day, increasing volume gradually.
• Respond to blocks: If a mailbox provider blocks, it's crucial to immediately cease increasing volume, reduce current send rates, and wait until the blocks subside.

Key considerations

• Implement IP warming: Even for existing IPs, if new throttling is experienced, treat it like a new IP warming cycle to build trust again.
• Prioritize authentication: Ensure all emails are fully authenticated with SPF, DKIM, and DMARC. This is fundamental for deliverability, especially on shared IPs, as detailed in our simple guide to DMARC, SPF, and DKIM.
• Gradual volume increase: Increase volume very slowly, for instance, by 12% every 2-3 days, for sensitive providers.
• Monitor for spam traps: Regularly clean lists to avoid hitting spam traps, which can severely damage sender reputation and lead to blocks or blocklist (blacklist) appearances. Our guide on email throttling for marketing covers this.

Key findings

• Gradual volume scaling: Spreading out email sends over a longer period is a recognized strategy to avoid or reduce rate limiting by mailbox providers.
• Sender reputation: Building and maintaining a strong sender reputation is paramount to prevent email throttling.
• Authentication standards: Proper email authentication with SPF, DKIM, and DMARC forms the backbone of a reliable email infrastructure.
• List quality: Cleaning databases and maintaining a clean email list by removing inactive or invalid contacts is crucial to avoid throttling and improve deliverability.
• IP warming: Warming up new IPs by gradually increasing sending volume is a widely recommended practice.

Key considerations

• Optimize sending speed: Adhering to recommended sending speeds and spacing out sends can significantly reduce throttling events. This aligns with advice on optimizing email sending speed.
• Standard opt-in processes: Implementing industry-standard opt-in processes helps build a healthy mailing list and avoid spam traps, as noted by Twilio's deliverability best practices.
• Monitor performance metrics: Continuously monitor bounce rates, complaint rates, and email delivery rates to maintain email list health.
• Reduce link redirects: Documentation suggests reducing redirects in email links and limiting requests from third-party domains to improve email performance and avoid potential flags.