Email deliverability for Seznam.cz and Centrum.cz: SPF, DKIM, DMARC and postmaster

If you target the Czech market, the bigger challenge than Gmail is Seznam.cz. Seznam mail filter has different IP reputation rules than Gmail, and Centrum.cz historically requires explicit postmaster registration. 4notify operates a dedicated CZ-geolocated IP, signs everything with 2048-bit DKIM and publishes DMARC with `reject` policy after a one-week reporting window.

Problem

Competitors route Czech mail through an Irish sendgrid IP. The result: Seznam tags 18% as promotions (graylisting) and Centrum drops straight to spam. You see 98% “delivered” in the report but open rate is 4% because nobody got it in the inbox.

Legal framework

Nařízení (EU) 2016/679 (GDPR) čl. 21

Data subject can object to direct marketing at any time — practically, list-unsubscribe must work in one click.

RFC 8058 — One-Click Unsubscribe

The List-Unsubscribe-Post: List-Unsubscribe=One-Click header is a soft requirement at Seznam since 2024 and a hard requirement at Gmail since 2024.

§ 7 zákona č. 480/2004 Sb. (ZSO)

Each commercial message must include a clear, free unsubscribe option — hence list-unsubscribe in every email.

Architecture

Dedicated CZ IP

Domain mail leaves from a CZ-geolocated IP, registered with postmaster.seznam.cz and abuse.seznam.cz.

SPF + DKIM 2048 + DMARC reject

Client adds three DNS records; we DKIM-sign every message with body hash so forwarders don't break the signature.

Feedback loop with Seznam

When a user clicks „spam“, Seznam sends an FBL message to our abuse@; 4notify catches it, marks the recipient as suppressed and excludes from future sends.

Gradual warm-up

First two weeks ramp from 200 messages/day exponentially so Seznam acclimatises to the new domain. Without warm-up, deliverability drops to 60%.

Code

txt
# DNS records to publish (Cloudflare / WEDOS / Forpsi / Active24):

@               IN  TXT  "v=spf1 include:_spf.4notify.net ~all"
default._domainkey IN TXT "v=DKIM1; k=rsa; p=MIIBIjANBgkqh... (2048-bit)"
_dmarc          IN  TXT  "v=DMARC1; p=quarantine; rua=mailto:[email protected]; pct=100; fo=1"

# After 7 days of reporting, switch p=quarantine → p=reject.

Sample message

EmailOrder confirmation 2026-CZ-0481

Hello, thank you for order 2026-CZ-0481 totalling 1,248 CZK incl. VAT. Estimated delivery: Friday 29 May. Tracking: yourbrand.cz/tracking/CZ0481.

Before launch

Publish SPF, DKIM, DMARC at the .cz registrar
Register the domain at postmaster.seznam.cz
Set up abuse@ and postmaster@ in MX (RFC 2142)
Run the 14-day warm-up
Watch DMARC reports for a week, then switch to p=reject
Verify List-Unsubscribe-Post one-click works

What 4notify does differently

Dedicated Czech IP registered with both Seznam and Centrum postmasters, plus FBL automation — not a shared European sendgrid IP.

FAQ

Do we need a dedicated domain just for transactional mail?

We recommend a subdomain (e.g. notify.yourbrand.cz). DMARC and IP reputation are then isolated from marketing, which historically has higher complaint rates.

How long does warming up a new domain take?

14 days for volumes below 50,000 messages/day; 28 days for higher volumes. After that we hit a stable 99%+ Seznam delivery.

What if we used to be on a Seznam blocklist?

We help with the delisting request via Seznam postmaster; typically within 5 working days. We recommend moving to a clean subdomain in parallel.