DNS tools
Check one record at a time
Five lookups, each on its own page. Every one of them explains what the record means and where the requirement comes from, rather than only printing what DNS returned.
These tools make DNS queries, so unlike the header analyzer they are not offline: the domain you type is sent to a public resolver. Nothing else is — no account, no logging of what you look up.
SPF checkerCheck a domain’s SPF recordReads the published SPF record and says what it actually authorises — including the lookup limit, which is the failure people hit without noticing.OpenDMARC checkerCheck a domain’s DMARC recordReads the policy and says what it asks receivers to do — and what it does not. Includes the DMARCbis tags, since the specification changed.OpenDKIM checkerCheck a DKIM keyLooks up the key at a selector you name. Selectors cannot be discovered from DNS, so leaving the field empty tries a list of common names instead — which is a guess, not a discovery.OpenMX lookupLook up a domain’s MX recordsShows which servers accept mail for the domain, and recognises a null MX for domains that deliberately receive none.OpenBlacklist checkCheck a domain’s mail servers against blocklistsResolves the domain’s MX hosts to their addresses and asks the blocklists that answer from a browser. A list that refuses the query is reported as unknown, never as clean.Open
Looking at a message rather than a domain?
These tools read what a domain publishes. If you want to know why one particular message failed, paste its header into the analyzer instead — it works out which check broke on that message, and it never leaves your browser.
Open the analyzer