How to resolve spam filtering issues with seznam.cz?
Michael Ko
Co-founder & CEO, Suped
Published 1 Jun 2025
Updated 16 Aug 2025
8 min read
Dealing with email deliverability issues can be incredibly frustrating, especially when it comes to a significant internet service provider like Seznam.cz in the Czech Republic. Many email marketers and businesses find their messages are consistently being sent to the spam folder, resulting in drastically low open rates, sometimes as much as 90% lower compared to other major providers like Gmail or Yahoo. This can severely hinder communication with a crucial segment of your audience.
The challenge often stems from Seznam.cz's stringent anti-spam measures and specific requirements that might differ from those of global email providers. While general email best practices apply, there are nuances when targeting the Czech market through Seznam.cz that require a more tailored approach. Simply following standard deliverability guidelines might not be enough to bypass their sophisticated filters.
I've encountered this situation countless times, where emails that perform well elsewhere struggle to reach the inbox at Seznam.cz. Resolving these spam filtering issues requires a deep dive into your email setup, content, and sending practices, alongside understanding Seznam.cz's particular demands. Let's explore the steps you can take to diagnose and fix these problems.
Understanding Seznam.cz's anti-spam policy
Seznam.cz has a proactive approach to combating unwanted mail, and their anti-spam policy has evolved over the years to become quite robust. As far back as 2015, Seznam.cz announced a tightening of their anti-spam policy, particularly emphasizing the need for proper email authentication for mass emails. This means that if your emails lack a valid digital signature or fail other authentication checks, they are highly likely to be filtered as spam (or junk mail).
Their system is designed to protect users from malicious content and unsolicited commercial emails. This often includes looking beyond basic email authentication to scrutinize sender reputation, content relevance, and user engagement. If your sending practices trigger any red flags, your emails will face significant deliverability challenges, leading to blocklisting (or blacklisting) from their inboxes.
One important factor is how Seznam.cz perceives the sender. They prioritize emails from trusted sources with a consistent sending history and good engagement metrics. Any sudden spikes in volume, high complaint rates, or bounces can negatively impact your sender reputation with them. Understanding these underlying principles is the first step toward improving your email delivery.
Seznam.cz's strict stance on authentication
Seznam.cz is known for being particularly strict about email authentication protocols. They have explicitly stated that emails without proper SPF and DKIM records will be treated with suspicion, often leading to immediate junk foldering or rejection. Ensuring your DNS records are correctly configured is fundamental to your deliverability success with them.
Essential authentication and technical configurations
To ensure your emails don't fall into the spam folder at Seznam.cz, proper email authentication is paramount. This includes Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC). These records tell recipient servers that your emails are legitimate and prevent spoofing.
Seznam.cz specifically requires both SPF and DKIM. SPF specifies which mail servers are authorized to send email on behalf of your domain, while DKIM provides a digital signature that verifies the email has not been tampered with in transit. Without these, your emails may be immediately flagged. I highly recommend reviewing a simple guide to DMARC, SPF, and DKIM to ensure you have them set up correctly.
DMARC builds upon SPF and DKIM, allowing you to specify a policy for how recipient servers should handle emails that fail authentication. While not explicitly stated as a hard requirement for deliverability at Seznam.cz, implementing DMARC provides an additional layer of security and visibility into your email sending, which can positively impact your sender reputation over time.
Example SPF recordDNS
v=spf1 include:_spf.example.com ~all
Authentication protocol
Purpose
Impact on Seznam.cz deliverability
SPF
Authorizes sending servers for your domain.
Required for basic trust. Lack of SPF will likely lead to spam foldering.
DKIM
Digitally signs emails to prevent tampering.
Mandatory for mass emails to avoid the spam folder.
DMARC
Policy and reporting for authentication failures.
Enhances reputation and provides insights, recommended for all senders.
Content and sender behavior considerations
Beyond technical configurations, the content of your emails and your sending behavior significantly influence deliverability at Seznam.cz. Even if your authentication is perfect, poor content or suspicious sending patterns can lead to emails being filtered into the spam or bulk folder. I've seen instances where subject lines containing special characters, excessive capitalization, or emojis were a direct cause of emails landing in the bulk folder instead of the inbox.
Maintaining a clean and engaged subscriber list is also crucial. Sending to unengaged users or, worse, to spam traps, will quickly degrade your sender reputation. Ensure you have clear consent for all recipients and regularly clean your lists to remove inactive or invalid addresses. High bounce rates or spam complaints are major red flags that Seznam.cz (and other ISPs) will notice.
Your overall sender reputation plays a massive role. Seznam.cz considers factors like user complaints, bounces, and whether your IP address or domain is present on any major blocklists (or blacklists). It's wise to proactively monitor your sender reputation and address any issues promptly. This includes understanding what happens when your domain is on an email blacklist and how to recover.
Good practices
Clear subject lines: Use concise, descriptive subject lines without excessive punctuation, capitalization, or emojis. Keep it professional and relevant.
List hygiene: Regularly clean your email lists to remove inactive subscribers and hard bounces. This helps maintain a healthy sending reputation.
Consent-based sending: Only send emails to users who have explicitly opted into your communications.
Reputation monitoring: Keep an eye on your sender reputation and address any issues like high spam complaint rates or blocklist appearances.
Bad practices
Spammy subject lines: Avoid using all caps, multiple exclamation marks, or symbols that might trigger spam filters.
Outdated lists: Sending to old or purchased email lists increases the risk of hitting spam traps and bounces.
Ignoring engagement: Continuously emailing unengaged subscribers can negatively impact your sender score.
High complaint rates: If users frequently mark your emails as spam, it signals poor sending practices to Seznam.cz.
Leveraging Seznam.cz postmaster tools and feedback loops
One of the most effective ways to understand and resolve deliverability issues with any major ISP is by utilizing their postmaster tools and feedback loops (FBLs). Seznam.cz offers its own postmaster tool, which can provide invaluable insights into your sending reputation and email performance specifically within their network. This includes data on spam complaints, reputation metrics, and potential blocking issues.
Accessing the Seznam.cz postmaster tool and feedback loop can be a bit challenging, as it sometimes requires a Czech mobile number for registration. If you face this hurdle, try reaching out to their support team via chat for assistance. Many have found success in getting an account set up this way. Once registered, these tools allow you to closely monitor how your emails are being received and quickly identify trends or issues.
Feedback loops are critical because they send you reports when a recipient marks your email as spam. This information is vital for maintaining a healthy sender reputation and promptly removing complaining users from your list. Ignoring FBL reports can lead to increased spam complaints and eventual blocklisting (or blacklisting).
Additionally, some older discussions mention that including the Precedence: bulk header might help with deliverability for some Czech providers, including Seznam.cz. While it's not a guaranteed fix and its current impact may vary, it doesn't hurt to test if other measures haven't yielded results. This header suggests to the receiving server that the email is part of a bulk mailing, which can sometimes influence filtering decisions.
Using Seznam.cz's postmaster tool
Registering your domains with the Seznam.cz Postmaster Tool is a crucial step for optimizing your email strategy for the Czech market. This free resource provides essential data that can help you understand your sending reputation and resolve deliverability issues proactively.
Views from the trenches
Best practices
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and pass validation checks for your sending domain.
Maintain a clean email list by regularly removing unengaged subscribers and hard bounces to improve sending reputation.
Monitor your subject lines for excessive capitalization, emojis, or special characters that could trigger spam filters.
Common pitfalls
Ignoring feedback loop (FBL) reports, which leads to continued sending to complaining users and worsening reputation.
Failing to implement or correctly configure all necessary email authentication standards, causing emails to be flagged as suspicious.
Sending emails with generic or 'spammy' content and subject lines that don't meet Seznam.cz's content filtering criteria.
Expert tips
If you face issues registering for the Seznam.cz postmaster tool due to regional requirements, contact their support via chat.
Consider adding the 'Precedence: bulk' header to your mass emails, as it might help signal legitimate bulk sending to Seznam.cz.
Focus on consistent email engagement to build a strong sender reputation with Seznam.cz, reducing the chance of filtering.
Expert view
Expert from Email Geeks says to investigate if this is a recent change in email behavior and to confirm that all authentication protocols are properly in place, as filtering can result from many factors.
2021-12-21 - Email Geeks
Expert view
Expert from Email Geeks says that while the 'precedence:bulk' header was once required by Centrum, registering domains with the Seznam postmaster tool and joining the Validity Universal FBL (which includes Seznam) provides useful information.
2021-12-22 - Email Geeks
Restoring deliverability to Seznam.cz in the Czech Republic
Resolving spam filtering issues with Seznam.cz requires a multifaceted approach, focusing on robust technical setup, careful content creation, and diligent list management. Prioritizing email authentication protocols like SPF and DKIM is non-negotiable for ensuring your messages are recognized as legitimate. Beyond technicalities, actively managing your sender reputation and adhering to content best practices are equally vital. Remember, an email's journey to the inbox is determined by more than just its sender, it also relies on many technical details. You can explore more about why your emails are going to spam.
Leveraging the Seznam.cz postmaster tools and feedback loops is a crucial step in gaining direct insight into your deliverability performance within their network. While overcoming registration challenges may require some persistence, the data provided is invaluable for continuous improvement. By taking these comprehensive steps, you can significantly improve your chances of reaching the inbox and achieving higher engagement rates with your Czech audience.
