Free tools
Email debugging tools for the moment after
Small tools for the moment something has already gone wrong. Paste what you have, get an answer, close the tab. No account needed.
Where it went
3 hops · app.example.org → inbound
Where the time went
total 2m 28s · slowest hop 2m 25s
What was decided
spf fail · dkim pass · dmarc pass
Example header block. Values shown are parsed from it, not stored.
Runs in your browser
Where a tool can do the work locally, it does. Nothing is uploaded, logged or stored.
No account needed
No signup, no email wall, no trial. Open the page, paste, read the answer.
Then close the tab
Each tool answers one question. Nothing to configure, nothing to come back to.
The bench
One instrument per question
Each tool reads one kind of evidence. The ones that are not built yet are still listed, so the bench shows the plan instead of a single orphaned page.
Headers and delivery
2 tools · 1 built
Email header analyzer
Paste a raw header block and see the delivery path, where the time went, and what SPF, DKIM and DMARC actually returned.
Bounce decoder
SoonPaste a bounce message and get the reason in plain English, with the specific thing to change.
Authentication
2 tools · 0 built
DMARC report analyzer
SoonUpload an aggregate report and read it as a table instead of raw XML.
Domain health check
SoonOne pass over MX, SPF, DKIM, DMARC and MTA-STS for a sending domain.
Testing
1 tool · 0 built
SMTP tester
SoonCheck that a host accepts a connection, negotiates TLS, and authenticates.
Inbox
1 tool · 0 built
Test inbox
SoonA throwaway mailbox for checking what your application actually sends.
Built and live
The header analyser
Every server adds its own line to the top of a message, so the record you are handed is written backwards. The analyser reverses it, measures the gap between each hop, and reads out what the receiving server decided.
It parses everything in your browser. There is no server route behind the page, so the header block never leaves your machine.
Open the toolExample block · a valid ARC chain explains the SPF failure
After the debugging
These tools reconstruct what Sendmux already records
Every tool here answers a question after the fact, from something you had to go and find. Sendmux keeps the route, the provider that accepted each message, the authentication result and the reason anything bounced, as structured data an agent can read without anyone pasting anything.