How to resolve spam filtering issues with seznam.cz?
Updated on 23 Jun 2026: We updated this guide with clearer Seznam.cz sender identity checks, Czech-domain segmentation, and safer recovery pacing.
To resolve spam filtering issues with Seznam.cz, 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, consistent From and Return-Path domains, and subject lines that do not look noisy. The header Precedence: bulk is worth testing for genuine bulk mail, but it is not the fix to bet 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. Treat opens as a symptom, then confirm the issue with seed inboxes, click logs, complaint data, bounce logs, queue behavior, 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. Separate Seznam traffic in reporting so its bounce rate, complaint rate, open trend, click trend, authentication pass rate, and queue behavior are visible. Include Seznam-related domains such as Email.cz and Post.cz in this review when they appear in the list, then break them out if behavior differs.
Seznam publicly said in 2015 that mass email without a valid DKIM signature would be rated as spam. That DKIM policy still shapes how Czech mailbox delivery should be troubleshot: authentication is a baseline requirement for mass mail.
- 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
Do not start by rewriting copy. 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. Avoid sending brand mail from free webmail domains because Seznam can treat that identity as weaker than a controlled brand domain.
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 basic 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, 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 the complete delivered message is inspected.
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. Seznam has filtered some campaigns more harshly when subjects use heavy emoji, all caps, excessive punctuation, or unusual symbols. That does not mean every Czech campaign needs plain text subjects. It means the test should change only the subject first.
Message fixes
- Subject: Test one plain subject against the current version before changing anything else.
- HTML: Avoid image-only content, hidden text, broken tags, tracking links that redirect too many times, and missing visible unsubscribe links.
- 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 shows a results button when the test is ready.
?/43tests passed
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.
Also track temporary 4xx deferrals, queue time, and delivery expiry by Seznam-domain group. If queue time grows, hold volume instead of increasing pressure while the next content or authentication test runs. Shorter queue time at the same volume is a better recovery signal than one higher delivered count.
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 Seznam.cz, Email.cz, Post.cz, and other Czech-domain traffic so the issue is measurable without blended provider averages.
- Suppress hard bounces, complainers, and long-term inactive recipients before the next test.
- Test a small authenticated campaign with one clean subject and a working unsubscribe path.
- Scale volume only after placement, complaints, queue time, and click data improve for that segment.
How Suped helps with the workflow
Suped is our DMARC and email authentication platform. 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.
Suped's product keeps DMARC monitoring, SPF and DKIM visibility, hosted SPF, hosted DMARC, hosted MTA-STS, automated issue detection, real-time alerts, and blocklist monitoring in one workflow. 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
Suped surfaces whether a new sender failed DKIM, an SPF record is close to the lookup limit, or a Seznam-heavy campaign started failing after a content change. It 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
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, keep Seznam.cz as its own reporting segment, alert on authentication changes, watch 4xx deferrals, and review complaints after every Czech campaign. That turns the next issue into a measurable maintenance task instead of another postmaster guessing exercise.
