The free tools, in one place
A free Email Header Analyzer that lives here, plus the rest of the DuoCircle catalog: DMARC, SPF, DKIM, BIMI, MTA-STS, and a domain authentication audit that runs them all in one pass. Free, no signup, hosted on the canonical product sites.
Email Header Analyzer
Paste raw email headers and instantly see the full delivery path with per-hop time delays, plus SPF, DKIM, and DMARC results. Parsed entirely in your browser, nothing uploaded.
- → Origin to final hop, oldest at the top, newest at the bottom
- → Time delay on every hop, color-coded so slow ones jump out
- → SPF, DKIM, DMARC, ARC chain, and DKIM signing domains in one view
DuoCircle hosts the rest of the free tooling on the canonical product site for each capability. DMARC tools live on dmarcreport.com because that is where DMARC Report runs. SPF tools live on autospf.com because that is where AutoSPF runs.
Authentication tooling hosted on DMARC Report, the multi-region G2 Category Leader for DMARC software.
DMARC Report Analyzer
Drop a DMARC aggregate report (RUA XML or .gz) and see senders, alignment, pass rates, and per-record detail. Parsed entirely in your browser.
DMARC Record Checker
Look up the DMARC record on any domain and see policy, alignment mode, and report destinations.
DMARC Record Generator
Build a syntactically correct DMARC record for any domain. Walks through policy, percentage, and reporting addresses.
DKIM Lookup
Resolve a DKIM selector and inspect the public key and any policy attributes published in DNS.
BIMI Checker
Verify BIMI publication on a domain. Validates the BIMI record, fetches the SVG, and reports VMC presence.
MTA-STS Checker
Check that a domain publishes a valid MTA-STS policy and that the policy is reachable over HTTPS.
Domain Authentication Checker
Run SPF, DKIM, DMARC, BIMI, and MTA-STS in one pass. The full authentication snapshot for a domain.
SPF tooling hosted on AutoSPF, the SPF management product built because the established vendor would not scale to a $4 per month customer.
SPF Record Lookup
Fetch and pretty-print the SPF record for any domain. Shows includes, redirects, and the resolved sender list.
SPF Checker
Validate that an IP or sender is permitted by a domain SPF record. Shows the include chain that grants or denies.
SPF Validator
Check an SPF record for syntax errors, lookup-count overruns (the 10-DNS-lookup limit), and policy ambiguity.
SPF Record Generator
Build a valid SPF record from your sender list. Flags 10-lookup-limit risks before you publish.
Free is the door, the relationship is the asset
Every tool above runs on the product site that owns the capability. The Email Header Analyzer lives here because Mailflow Monitoring is where continuous mail-flow forensics runs. Use the tools as long as you want, free, no signup. When the free version stops scaling, the paid product is one click away on the same site.
We do not gate the tools, we do not require an email, and we do not store the data you put through them. The Email Header Analyzer in particular parses your headers entirely in your browser. Open DevTools and watch the Network tab if you want to verify it.
Need continuous monitoring instead of one-off forensics?
Mailflow Monitoring exercises your real delivery path on an interval and alerts on hops that slow down before users notice.