Koltrix
Free tools
Diagnose your email, without an account.
No signup, no email capture, nothing stored. We built these because we needed them.
SPF, DKIM & DMARC checker
The three records that decide whether your email arrives — checked, explained, and with the fix for each problem.
Open →MX lookup
Where a domain's mail is delivered, in priority order, and whether there is a fallback.
Open →Email header analyzer
The full delivery path, hop by hop, with authentication results and where the time went. Runs in your browser.
Open →Why there is no blocklist checker
The major blocklists — Spamhaus among them — refuse lookups that come from public resolvers or shared cloud infrastructure, and answer with a “query refused” code rather than a real result. A checker built on that would confidently tell you that you are not listed when it had not actually been allowed to ask.
Doing it properly needs a paid data feed and a dedicated resolver, which is not the sort of thing that belongs in a free tool. So it is not here, rather than here and wrong.