Verifying Seznam addresses

• Unknown local parts return a clean 550 with consistent wording.
• Rate limits are reasonable and a steady probe rate gets steady answers.
• The email.cz and post.cz domains are Seznam brands on the same infrastructure.
• Seznam holds a genuinely dominant position locally, so a Czech consumer list concentrates here rather than spreading across providers.

• Seznam competes with Google locally and retains a large share of Czech consumer email.
• Czech-language content and a local sending reputation both help with this audience.
• Diacritics in Czech names reach local parts occasionally and need correct encoding.

You can confirm the Seznam family yourself. On September 19, 2026 we ran dig MX against each of its domains. seznam.cz returned mx1.seznam.cz at priority 10 and mx2.seznam.cz at 20. email.cz and post.cz returned the same two hosts at priorities 5 and 10. spoluzaci.cz, left over from a classmates site, returned them as well.

Say a Prague e-shop hands you 8,000 customer rows and 5,200 are spread across those four domains. For planning purposes that's one queue to one operator, not four small ones. It also sets your expectation for the report. With most of the list sitting on a provider that answers directly, coverage should come out high, and if it doesn't, look for a block on the probing side before you blame the data. A block shows up as the same refusal on row after row, while bad data fails one address at a time with ordinary rejections.

Czech lists carry a second family of freemail domains that people lump in with Seznam. In the same lookup, centrum.cz, atlas.cz and volny.cz all pointed at hosts under eco-mx.cz, with names like centrum-cz-10mx1.eco-mx.cz. That's a different operator with its own servers, its own limits and its own reputation system.

It matters when something goes wrong. If your Seznam rows resolve and your Centrum rows come back unknown, that's two providers behaving differently, which is normal. Had you filed them together as Czech freemail, the same result looks like random failure inside one group and sends you hunting for a bug that isn't there. Build provider groups from MX hostnames, never from country codes, and give each group its own line in the bounce report after every send.