Mailbox provider · Seznam
How to verify a seznam.cz email address
Can you verify @seznam.cz addresses?
YesYes. @seznam.cz answers mailbox checks one address at a time.
Check one address
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The checker opens an SMTP conversation with seznam.cz's mail server, offers a random address first to rule out a catch-all, then names your address at RCPT TO and disconnects without sending. A rejection comes back invalid ("Mailbox not found") and an acceptance valid ("Mailbox exists"). Temporary replies come back risky. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
Mailbox existsMailbox not foundServer would not confirmSeznam addresses can be verified without sending an email. On 12 October 2026 the seznam.cz mail server mx1.seznam.cz rejected a made-up recipient at the SMTP RCPT TO step with 550 5.1.1 sorry, no such mailbox here, so a mailbox check can tell a missing seznam.cz account from a real one.
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Live DNS snapshot: seznam.cz
Checked 6 November 2026, 12:15 UTCRead from DNS at the time shown and refreshed at most once a day. MX says where mail for seznam.cz goes; SPF and DMARC describe mail sent from it, not whether any one address exists.
- 10
mx1.seznam.cz - 20
mx2.seznam.cz
v=spf1 mx ip4:77.75.78.0/23 ip4:77.75.76.0/23 ip6:2a02:598::/32 ?allp=none: meets the requirement, but blocks nothing.
v=DMARC1; p=none; sp=reject; rua=mailto:[email protected]Look up any other domain with the MX lookup or the email provider lookup.
Seznam at a glance
| Operated by | Seznam.cz, a. s., Prague, Czech RepublicSource: Email.cz terms of service (Czech) |
|---|---|
| MX hosts | mx1.seznam.cz, then mx2.seznam.czObserved 12 October 2026 (dig MX) |
| Answer to a made-up address | 550 5.1.1 sorry, no such mailbox here, returned at RCPT TOObserved 12 October 2026 (SMTP probe of a made-up recipient, no message sent) |
| Inactive accounts | Seznam may block a mailbox never used in the 14 days after creation, or one not logged into for more than 6 monthsSource: Email.cz terms, clause 3.6 (Czech) |
| Postmaster rules | Valid SPF and DKIM are required for delivery; DMARC is strongly recommendedSource: Seznam for senders: authentication (Czech) |
| Postmaster rules | Bulk senders should use double opt-in and delete non-existent and inactive contactsSource: Seznam for senders: contact lists (Czech) |
What Seznam's server says about a missing mailbox
The reply that matters is the one to RCPT TO, the step where the checking server names the recipient. Seznam answered our made-up seznam.cz address with 550 5.1.1 sorry, no such mailbox here. A 5xx code at that step is a permanent "no such mailbox", which is the same answer a real message would get, so SimpleVerifier marks the address invalid with the reason "Mailbox not found". A 250 at the same step means the mailbox exists and comes back valid.
Before trusting a "valid", a careful verifier also offers a random address that cannot exist. Seznam rejected ours, so seznam.cz is not a catch-all: a 250 for your address is a real signal. Temporary 4xx replies (421, 450, 451) are about the connection, not the mailbox, and come back risky with "Server would not confirm" rather than invalid. Hard bounce vs soft bounce explains why that split matters.
Seznam closes unused mailboxes fast
The Email.cz terms let Seznam block a mailbox that was never used in its first 14 days, or one its owner hasn't logged into for more than six months. Sign-ups that gave a fresh @seznam.cz address and never engaged are worth re-checking before a campaign.
Seznam's guidance for bulk senders is direct: confirm contacts with double opt-in and delete non-existent and inactive ones. Its authentication page adds that valid SPF and DKIM are required for delivery.
Cleaning seznam.cz addresses on a list
Because Seznam answers honestly, seznam.cz is one of the domains where verification removes bounces before they happen. Drop the invalid results, keep the valid ones, and re-check the risky ones later: a temporary reply on one day often turns into a clear answer the next.
A valid result only means the mailbox exists today. Addresses on an old consumer list go stale as people stop using them, so re-verify before each large send to an aged segment; how often to verify an email list gives a schedule. Upload the CSV to the verifier and download the valid, risky and invalid rows as separate files.
Common questions
- Can you verify @seznam.cz addresses?
- Yes. @seznam.cz answers mailbox checks one address at a time. The checker opens an SMTP conversation with seznam.cz's mail server, offers a random address first to rule out a catch-all, then names your address at RCPT TO and disconnects without sending. A rejection comes back invalid ("Mailbox not found") and an acceptance valid ("Mailbox exists"). Temporary replies come back risky. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
- Can I check if a seznam.cz address exists without emailing it?
- Yes. A verifier connects to Seznam's mail server, names the address at the RCPT TO step and disconnects before sending. On 12 October 2026 the server rejected a made-up seznam.cz address with "550 5.1.1 sorry, no such mailbox here", so a missing mailbox shows up as invalid and the owner receives nothing.
- What mail servers does seznam.cz use?
- On 12 October 2026, seznam.cz published these MX hosts: mx1.seznam.cz, then mx2.seznam.cz. You can look them up yourself with the free MX lookup tool.
- Why did a seznam.cz address come back risky instead of invalid?
- Risky means the server didn't give a permanent answer during the check, usually a temporary 4xx reply or a timeout. It isn't proof the address is bad. Check it again later; Seznam gave a clear rejection for a missing mailbox when we tested it.
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