Mailbox provider · Seznam
How to verify a seznam.cz email address
Seznam 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.
Mailbox checks: Verifiable. The server rejects unknown recipients during the SMTP conversation.
Seznam at a glance
| 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) |
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.
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.
Live DNS check for seznam.cz
These are seznam.cz's own sending records, refreshed daily. They describe mail sent from the domain, not whether a given address at it exists.
4 of 5 checks passed
80%Blocklist status
Not listed on SURBL, SpamCop
DKIM — message signing
No DKIM found on common selectors — it may use a custom one
DMARC — spoofing policy
DMARC set to reject — strongest protection
Mail servers (MX)
2 mail server(s), primary mx1.seznam.cz
SPF — authorised senders
SPF present, neutral (?all) — provides little protection
Common questions
- 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.
Check a Seznam address
The free checker runs the mailbox check on one address and shows the server's reason, so you can see which of the cases above applies.