How to resolve spam filtering issues with seznam.cz?
Michael Ko
Co-founder & CEO, Suped
Published 1 Jun 2025
Updated 22 May 2026
8 min read
Summarize with
To resolve spam filtering issues with Seznam.cz, I start with the items Seznam is known to care about most: valid DKIM on bulk mail, SPF authorization, DMARC reporting, a stable sender identity, clean consent, and subject lines that do not look noisy. The header Precedence: bulk is worth testing, but it is not the fix I would bet the recovery on.
A 90% lower open rate at Seznam than Gmail or Yahoo usually means one of two things: mail is landing in the bulk folder, or Seznam is loading tracking images differently for that audience. I treat opens as a symptom, then confirm the issue with seed inboxes, click logs, complaint data, bounce logs, and real message headers.
Fast answer
Fix authentication first, register for Seznam feedback data, simplify subject lines, isolate Czech recipients into a cleaner sending segment, and contact Seznam only after you have exact IPs, domains, headers, dates, and remediation steps. A postmaster message without evidence rarely moves the case forward.
What Seznam filters first
Seznam.cz is a local mailbox provider with its own filtering behavior, not a smaller clone of Gmail. That matters because a sender can look healthy in global reporting while still performing poorly at Seznam. I separate Seznam traffic in reporting so I can see its own bounce rate, complaint rate, open trend, click trend, and authentication pass rate.
Seznam publicly said in 2015 that mass email without a valid DKIM signature would be rated as spam. That DKIM policy still shapes how I troubleshoot Czech mailbox delivery: authentication is not a nice extra, it is table stakes.
- DKIM Use a dedicated DKIM signing domain for the sender, not a shared or generic signature.
- SPF Authorize the sending IPs and keep the record under the DNS lookup limit.
- DMARC Collect reports and confirm the visible From domain matches an authenticated domain under DMARC rules.
- Reputation Track complaints, bounces, inactive recipients, and any blocklist or blacklist listing for the sending IP.
A six-step Seznam.cz troubleshooting path covering DKIM checks and volume recovery.
Fix authentication before content
I do not start by rewriting copy. I start with DNS and headers because Seznam has a clear history of enforcing sender authentication for mass mail. If the message fails DKIM, if SPF is broken, or if DMARC reports show unknown sources using the domain, content tweaks will not compensate.
Run a domain health check for the exact From domain, then compare it with the domain in the DKIM d= value and the Return-Path domain. If those domains are not under your control, or they are inconsistent across campaigns, fix that before asking Seznam for help.
Minimum DNS baselineDNS
example.com TXT "v=spf1 include:send.example.net -all" selector1._domainkey.example.com TXT "v=DKIM1; k=rsa; p=MIIB..." _dmarc.example.com TXT "v=DMARC1; p=none; rua=mailto:dmarc@example.com"
Do not skip the boring checks
The sending IP needs valid reverse DNS, the HELO name needs to make sense, the visible From domain needs MX records, and the reply address needs to work. These checks sound basic because they are basic, but local providers often penalize sloppy infrastructure faster than large global providers.
|
|
|
|---|---|---|
DKIM | Valid pass | Use dedicated key |
SPF | Lookup count | Trim includes |
DMARC | Matched domain | Read reports |
rDNS | IP name | Fix PTR |
A compact Seznam troubleshooting matrix.
Test the message Seznam receives
Once DNS is clean, I test the actual email. A record can pass while a campaign still looks risky because the subject, HTML, tracking domains, reply path, unsubscribe path, or image mix sends the wrong signals. Seznam filtering issues often show up only when you inspect the complete delivered message.
Send the exact campaign to an email tester and to a real Seznam.cz mailbox. Compare the headers, placement, links, image loading, and final HTML. If the test email passes but the campaign performs badly, the problem is audience quality, volume, cadence, or the specific content variant.
Email tester sample report showing total score, email preview, issue summary, and per-section results
The subject line test deserves its own pass. I have seen Seznam behave more harshly with emoji-heavy subjects, all caps, excessive punctuation, and unusual symbols. That does not mean every Czech campaign needs plain text subjects. It means you should run an A/B test where only the subject changes.
Message fixes
- Subject Test one plain subject against the current version before changing anything else.
- HTML Avoid image-only content, hidden text, broken tags, and tracking links that redirect too many times.
- Headers Add List-Unsubscribe and test Precedence: bulk only for real bulk mail.
Sender fixes
- Identity Keep the same From address for a stream so Seznam can build history.
- Replies Use a monitored reply address instead of no-reply for marketing streams.
- Volume Send to active Czech recipients first, then expand only when complaint data stays clean.
Email tester
Send a real email to this address. Suped opens the report when the test is ready.
?/43tests passed
Preparing test address...
Use that test result as a baseline, then change only one thing at a time. If the next send adds a new subject, a new template, and a new sender domain, you lose the ability to tell which change helped or hurt Seznam placement.
Use feedback data instead of guessing
Seznam has a feedback loop path for senders. If you can register, use it. If registration needs a local account or phone verification, ask the Czech customer or local business owner to help create the account, then route the feedback data into your suppression process.
Feedback loop data tells you who complained, but it does not explain every filtering decision. Pair it with DMARC aggregate data, bounce logs, engagement by domain, and blocklist monitoring. A blacklist or blocklist hit on the sending IP is not always the root cause at Seznam, but it is evidence you need before escalating.
Recovery gates for Seznam traffic
Use these practical gates before scaling Czech mailbox volume again.
Healthy
Pass plus under 0.1%
Authentication passes and complaints stay low.
Watch
0.1-0.3%
Complaints, bounces, or spam-folder tests need review.
Pause
Over 0.3%
Stop broad sends and repair list quality.
- Segment Create a Seznam.cz and Czech-domain segment so you can measure the issue without blended provider averages.
- Suppress Remove hard bounces, complainers, and long-term inactive recipients before the next test.
- Test Send a small authenticated campaign with one clean subject and a working unsubscribe path.
- Scale Increase volume only after placement, complaints, and click data improve for that segment.
How Suped helps with the workflow
Suped is our DMARC and email authentication platform, and this is exactly the kind of workflow it is built to simplify. For Seznam issues, the practical job is to see every source using the domain, prove DKIM and SPF are passing, spot failures in real time, and connect those failures to specific sending services.
For most teams, Suped is the strongest practical choice because it combines DMARC monitoring, SPF and DKIM visibility, hosted SPF, hosted DMARC, hosted MTA-STS, automated issue detection, real-time alerts, and blocklist monitoring in one place. MSPs also get multi-tenant reporting, which matters when several Czech customers are affected at once.
Issue steps to fix dialog showing the issue overview, tailored fix steps, and verification action
The point is not to stare at raw XML. The point is to know that a new sender failed DKIM yesterday, that an SPF record is close to the lookup limit, or that a Seznam-heavy campaign started failing after a content change. Suped turns those signals into an issue list with steps to fix and verification actions.
Practical Suped setup
Add the sending domain, enable DMARC reporting, verify SPF and DKIM, turn on alerts for authentication drops, and monitor Seznam-heavy campaigns separately. If DNS changes are slow inside your organization, hosted SPF and hosted DMARC reduce the amount of direct DNS editing needed after setup.
When to contact Seznam
Contacting Seznam is worth doing, but only after you have evidence. A vague request for whitelisting is weak. A concise technical report gives the postmaster or support team something specific to inspect.
- Identifiers Include sending IPs, From domains, DKIM selectors, Return-Path domains, and campaign IDs.
- Evidence Attach full headers, timestamps, SMTP responses, and examples of Seznam-only poor placement.
- Remediation State exactly what you fixed: DKIM, SPF, list hygiene, subject tests, and volume reduction.
- Ask Request review of the listed IPs and domains rather than asking for a generic unblock.
Header test for true bulk mailtext
Precedence: bulk List-Unsubscribe: <mailto:unsubscribe@example.com> List-Unsubscribe-Post: List-Unsubscribe=One-Click
I only add Precedence: bulk where the message is genuinely bulk or marketing mail. For transactional mail, focus on authentication, stable routing, and relevance. Mixing marketing and transactional streams on the same IP or From domain makes Seznam troubleshooting harder.
Views from the trenches
Best practices
Keep Seznam traffic on stable senders and review DKIM, SPF, DMARC, rDNS, and HELO together.
Register for Seznam feedback data early, then route complaints into suppression rules.
Change one variable per test so subject, header, content, and sender changes stay readable.
Common pitfalls
Adding Precedence: bulk without fixing DKIM leaves the main Seznam risk untouched.
Using emoji-heavy subjects can hide improvements by triggering separate content filtering.
Waiting for a postmaster reply before fixing list quality wastes time during recovery.
Expert tips
Test subject lines without emojis, all caps, or symbols before changing infrastructure.
Ask a Czech customer to help with account verification when Seznam signup blocks access.
Separate transactional and marketing streams before judging whether Seznam dislikes the brand.
Marketer from Email Geeks says Seznam filtering should be investigated with feedback data, authentication checks, consent review, targeting review, and recent change history before making header changes.
2021-12-22 - Email Geeks
Marketer from Email Geeks says the Precedence: bulk header is low risk to test, but it should not be treated as a magic fix for inbox placement.
2021-12-22 - Email Geeks
The practical fix
The best way to fix Seznam.cz spam filtering is to remove uncertainty in order. Prove DKIM, SPF, and DMARC are correct. Prove the message itself is clean. Prove the Seznam audience has consent and recent engagement. Prove the sending IP and domain are not listed on a major blocklist or blacklist. Then scale volume slowly.
The Precedence: bulk header belongs in the test plan, not at the center of the plan. Seznam has signaled that authentication and sender quality matter. If those are weak, a header change will not rescue the campaign.
For ongoing prevention, I would keep Seznam.cz as its own reporting segment, alert on authentication changes, and review complaints after every Czech campaign. That turns the next issue into a measurable maintenance task instead of another postmaster guessing exercise.
