What are the best practices for sending email to Polish providers like Interia to avoid throttling?
Michael Ko
Co-founder & CEO, Suped
Published 12 Jul 2025
Updated 16 Aug 2025
7 min read
Sending emails to Polish email providers, particularly services like Interia, can present unique challenges, especially regarding email throttling. I've seen firsthand how these providers can be quite strict, often delaying or even rejecting email volumes that might be accepted elsewhere. It's a common concern for senders, particularly those operating on shared IP addresses.
The key to successful email delivery in Poland, and indeed across many European mailbox providers, lies in understanding and respecting their specific practices. This often means adjusting your sending strategy beyond general best practices, focusing on volume, authentication, and recipient engagement. Let's delve into the specific actions you can take to ensure your emails reach Polish inboxes without significant delays.
What email throttling means
Email throttling is a common tactic used by mailbox providers (MBPs) to manage incoming email volume and protect their users from spam. When an ISP (Internet Service Provider) throttles your emails, it means they are temporarily delaying your messages, allowing only a certain number through within a specific timeframe. This can lead to significant queue times and even email expiration if the message isn't delivered within the sender's retry window.
Polish providers, including Interia, are known for their particularly strict approach to incoming mail. Unlike some larger global ISPs that might have more flexible policies, Polish MBPs often implement tighter controls, which can result in heavy throttling even for moderate sending volumes. This is frequently linked to their assessment of your sender reputation and how well your email adheres to their specific, sometimes unstated, rules.
The challenge is that these throttling measures don't always come with clear bounce messages, making it difficult to pinpoint the exact cause. You might simply see messages stuck in a queue until their delivery time expires. This necessitates a proactive approach to your sending practices rather than a reactive one based on bounce codes. Understanding how to handle email sending rate limits is crucial.
How email throttling works
Email throttling occurs when an Internet Service Provider (ISP) or mailbox provider intentionally limits the rate at which it accepts emails from a particular sender or IP address. This is a defense mechanism against spam, abuse, and network overload. When your emails are throttled, they are not immediately rejected, but rather queued for later delivery.
Rate limits: ISPs set specific limits on the number of connections, messages per connection, or messages per hour from a given IP. Exceeding these triggers throttling.
Sender reputation: A low sender score (due to spam complaints, bounces, or low engagement) leads to stricter throttling or even blacklisting.
Content analysis: Suspicious content, links, or formatting can flag your emails for throttling.
Building a strong sender reputation
A strong sender reputation is paramount for avoiding email throttling, especially with discerning providers like Interia. This reputation is largely built on how well your emails are authenticated and the consistency of your sending practices. Many European providers, including those in Poland, place a significant emphasis on proper email authentication.
Ensure your domain has correctly configured SPF, DKIM, and DMARC records. These protocols prove that your emails are legitimate and prevent unauthorized parties from sending emails on your behalf. Polish MBPs (mailbox providers) are known to prefer fully authenticated mail. For instance, some Polish providers are particular about authentication as a factor in their deliverability decisions. You can learn more about DMARC, SPF, and DKIM to set them up correctly.
For shared IP environments, where many senders use the same IP, proper authentication becomes even more critical. While an IP's overall reputation can affect you, strong domain-level authentication helps Interia and other providers distinguish your mail from others on the shared IP. This includes having CNAME records for return-path domains, which German providers like GMX also prefer for better domain alignment.
Consistency in your sending volume and frequency also contributes to a stable sender reputation. Erratic sending patterns (e.g., sending huge volumes after long periods of inactivity) can trigger spam filters and throttling. Instead, aim for a predictable sending cadence, allowing MBPs to learn and trust your sending behavior. This is a core part of email sending speed best practices.
Strategic sending volume and IP warming
One of the most impactful strategies for Polish providers is cautious volume management. Many email deliverability experts recommend starting with a low volume for any new sending to Polish MBPs. A common guideline is to begin with around 1,000 messages per day per mailbox provider.
After establishing this initial baseline, gradually increase your sending volume. A recommended rate is to increase by no more than 10-15% every 2-3 days. This gradual ramp-up, often referred to as IP warming, allows the mailbox provider's systems to build a positive reputation for your sending IP and domain. If you encounter blocks or significant throttling, it's crucial to pause volume increases and potentially reduce your sending until the issues subside. This measured approach is vital for warming up an IP address.
It's important to note that even relatively low volumes can experience throttling with Polish providers. For example, some senders report significant queue times even when sending less than 10,000 emails over several days on a high-volume shared server. This highlights their sensitivity and the need for careful, consistent volume adjustments.
Furthermore, some Polish providers may have a 'pay-to-play' model or certification programs, such as the Trusted Sender program. While not always a viable option for all senders, it indicates their approach to managing email flow and reputation. Prioritize organic reputation building through best practices first, but be aware of such programs as an additional consideration for very high-volume sending. This approach can help staggering email sends to improve reputation.
Day
Initial volume
Interia Volume (+12%)
1-2
1,000
1,000
3-4
1,120
1,120
5-6
1,254
1,254
7-8
1,404
1,404
Content, engagement, and list hygiene
Even with perfect technical setup and volume management, the quality of your email list and the content you send can significantly impact deliverability and throttling. Polish providers, like others, prioritize mail that is relevant and engaging to recipients.
Regularly clean your email lists to remove inactive, invalid, or bouncing addresses. Sending to a high percentage of bad addresses can quickly damage your sender reputation and trigger blocklists (or blacklists), leading to throttling. High bounce rates signal poor list hygiene to ISPs. Additionally, avoid sending to purchased or old lists, as these often contain spam traps which severely harm your reputation. If you're on a blocklist, understand what happens when your domain is on an email blacklist.
Focus on sending personalized, relevant content that encourages engagement (opens, clicks, replies) and minimizes spam complaints. Low engagement rates and high complaint rates are red flags that can cause throttling. Implement clear unsubscribe options and honor them promptly. Prioritizing these best practices is crucial for avoiding spam filters and ensuring your messages reach the inbox.
Prioritizing active engagement
Instead of focusing solely on sending volume, prioritize sending to your most engaged subscribers first. This builds a positive sending history with ISPs and improves your sender reputation. Engaged recipients are less likely to mark your emails as spam, which signals to the ISP that your mail is wanted.
Segment your lists: Target active users with more frequent or premium content.
Re-engagement campaigns: Try to re-engage dormant subscribers before removing them.
Opt-in processes: Use double opt-in to ensure subscribers genuinely want your emails.
Views from the trenches
Best practices
Start with very low sending volumes (e.g., 1,000 emails/day) to Polish mailbox providers like Interia and gradually increase by 10-15% every 2-3 days, closely monitoring for any throttling or blocks.
Ensure all your emails are fully authenticated with SPF, DKIM, and DMARC to build trust and demonstrate legitimacy, as Polish providers prioritize well-authenticated mail streams.
Maintain exceptional list hygiene by regularly removing unengaged subscribers and invalid addresses to prevent high bounce rates and spam complaints.
Segment your audience and prioritize sending to your most engaged recipients first, signaling positive sender behavior to mailbox providers.
Common pitfalls
Sending high volumes of email too quickly to Polish providers without proper warming, leading to immediate and severe throttling or outright blocks.
Neglecting email authentication (SPF, DKIM, DMARC), which Polish mailbox providers often use as a primary filter for incoming mail.
Failing to clean email lists, resulting in high bounce rates and increased spam trap hits, which significantly damage sender reputation.
Ignoring low engagement metrics, as Polish providers interpret disinterest as a sign of unwanted mail, triggering throttling mechanisms.
Expert tips
Polish providers may have a 'pay-to-play' model, allowing for increased volume limits through direct payment or certification programs. While not always ideal, it's a factor to consider for strategic, high-volume sending.
In shared IP environments, your authentication and domain alignment become even more crucial as they help distinguish your mail from other senders on the same IP.
Throttling from Polish providers often manifests as prolonged queue times rather than specific bounce messages, requiring vigilance in monitoring delivery logs.
Even relatively low sending volumes can experience significant throttling, underscoring the importance of a meticulous warm-up process tailored to these specific providers.
Marketer view
Marketer from Email Geeks says to start with 1,000 messages per day in Poland for any mailbox provider, and then increase volume by 12% every 2-3 days. If blocking occurs, the sender should reduce volume and wait until the blocking stops.
2021-10-13 - Email Geeks
Expert view
Expert from Email Geeks says that European providers tend to throttle more aggressively and prefer domain alignment and authentication, which is crucial for deliverability.
2021-10-14 - Email Geeks
Sustaining long-term deliverability
Dealing with email throttling from Polish providers like Interia requires a strategic and patient approach. It's not just about raw volume, but also about building a trusted sender reputation through consistent authentication, careful IP warming, and diligent list management. By adhering to these best practices, you can significantly improve your chances of reaching the inbox without frustrating delays. Consistent monitoring and adaptation are essential for improving email deliverability.
Remember, email deliverability is an ongoing process. Regular auditing of your sender reputation, including checking for any unexpected blocklist (or blacklist) placements, will help you maintain a healthy sending environment. Adjust your strategies based on performance metrics and continue refining your approach to keep your emails flowing smoothly.
