Authentication
SPF
Verifies that the connecting IP is authorised to send for the envelope domain.
Free SMTP server diagnostics
Test your mail server, live
Send a test email from the server you want to diagnose. We capture the SMTP session, verify SPF, DKIM, DMARC, ARC, and seven more checks — while you watch every command and reply stream in real time.
How it works
Get a test address
We create a temporary inbox just for you. Copy the address and host shown on screen — it stays active for 10 minutes.
Send from your server
Send a test email from the server or application you want to diagnose. The SMTP session streams live as your server connects.
Read the full report
SPF, DKIM, DMARC, PTR, blocklists, spam scores and more — all verified against the actual message your server delivered.
What we check
Every check runs against the message your server actually delivered — no guesswork, no assumptions.
Authentication
DKIM
Cryptographically re-verifies the signature against the public key in DNS — not just what the receiving server reported.
Authentication
DMARC
Checks alignment of SPF and DKIM results against the From domain and evaluates the published policy.
Authentication
ARC
Validates the Authenticated Received Chain — essential for diagnosing DMARC failures through forwarders and mailing lists.
Infrastructure
PTR / rDNS
Confirms the connecting IP has a reverse DNS record and that it forward-confirms (FCrDNS), then checks consistency with the HELO domain.
Infrastructure
List-Unsubscribe
Checks RFC 2369 compliance and one-click unsubscribe support per RFC 8058 — required by Gmail and Yahoo for bulk senders.
Reputation
IP Blocklists
Checks the connecting IP against multiple DNS-based blocklists (DNSBL).
Reputation
Domain Blocklists
Checks the sender's From domain against domain reputation lists (RHSBL) — an angle most tools miss.
Reputation
Domain Age
Looks up when the sender domain was registered. Newly-registered domains carry elevated spam risk.
Content
Rspamd
Submits the full message to Rspamd — the dominant filter in self-hosted mail stacks — and maps the score to a verdict.
Content
SpamAssassin
Runs the message through SpamAssassin alongside Rspamd, so you see both perspectives in one run.
Authentication
BIMI
Checks whether the sender's domain publishes a BIMI record and validates any attached Mark Certificate (VMC).
Authentication
SPF
Verifies that the connecting IP is authorised to send for the envelope domain.
Authentication
DKIM
Cryptographically re-verifies the signature against the public key in DNS — not just what the receiving server reported.
Authentication
DMARC
Checks alignment of SPF and DKIM results against the From domain and evaluates the published policy.
Authentication
ARC
Validates the Authenticated Received Chain — essential for diagnosing DMARC failures through forwarders and mailing lists.
Infrastructure
PTR / rDNS
Confirms the connecting IP has a reverse DNS record and that it forward-confirms (FCrDNS), then checks consistency with the HELO domain.
Infrastructure
List-Unsubscribe
Checks RFC 2369 compliance and one-click unsubscribe support per RFC 8058 — required by Gmail and Yahoo for bulk senders.
Reputation
IP Blocklists
Checks the connecting IP against multiple DNS-based blocklists (DNSBL).
Reputation
Domain Blocklists
Checks the sender's From domain against domain reputation lists (RHSBL) — an angle most tools miss.
Reputation
Domain Age
Looks up when the sender domain was registered. Newly-registered domains carry elevated spam risk.
Content
Rspamd
Submits the full message to Rspamd — the dominant filter in self-hosted mail stacks — and maps the score to a verdict.
Content
SpamAssassin
Runs the message through SpamAssassin alongside Rspamd, so you see both perspectives in one run.
Authentication
BIMI
Checks whether the sender's domain publishes a BIMI record and validates any attached Mark Certificate (VMC).
Authentication
SPF
Verifies that the connecting IP is authorised to send for the envelope domain.
Authentication
DKIM
Cryptographically re-verifies the signature against the public key in DNS — not just what the receiving server reported.
Authentication
DMARC
Checks alignment of SPF and DKIM results against the From domain and evaluates the published policy.
Authentication
ARC
Validates the Authenticated Received Chain — essential for diagnosing DMARC failures through forwarders and mailing lists.
Infrastructure
PTR / rDNS
Confirms the connecting IP has a reverse DNS record and that it forward-confirms (FCrDNS), then checks consistency with the HELO domain.
Infrastructure
List-Unsubscribe
Checks RFC 2369 compliance and one-click unsubscribe support per RFC 8058 — required by Gmail and Yahoo for bulk senders.
Reputation
IP Blocklists
Checks the connecting IP against multiple DNS-based blocklists (DNSBL).
Reputation
Domain Blocklists
Checks the sender's From domain against domain reputation lists (RHSBL) — an angle most tools miss.
Reputation
Domain Age
Looks up when the sender domain was registered. Newly-registered domains carry elevated spam risk.
Content
Rspamd
Submits the full message to Rspamd — the dominant filter in self-hosted mail stacks — and maps the score to a verdict.
Content
SpamAssassin
Runs the message through SpamAssassin alongside Rspamd, so you see both perspectives in one run.
Authentication
BIMI
Checks whether the sender's domain publishes a BIMI record and validates any attached Mark Certificate (VMC).
Authentication
SPF
Verifies that the connecting IP is authorised to send for the envelope domain.
Authentication
DKIM
Cryptographically re-verifies the signature against the public key in DNS — not just what the receiving server reported.
Authentication
DMARC
Checks alignment of SPF and DKIM results against the From domain and evaluates the published policy.
Authentication
ARC
Validates the Authenticated Received Chain — essential for diagnosing DMARC failures through forwarders and mailing lists.
Infrastructure
PTR / rDNS
Confirms the connecting IP has a reverse DNS record and that it forward-confirms (FCrDNS), then checks consistency with the HELO domain.
Infrastructure
List-Unsubscribe
Checks RFC 2369 compliance and one-click unsubscribe support per RFC 8058 — required by Gmail and Yahoo for bulk senders.
Reputation
IP Blocklists
Checks the connecting IP against multiple DNS-based blocklists (DNSBL).
Reputation
Domain Blocklists
Checks the sender's From domain against domain reputation lists (RHSBL) — an angle most tools miss.
Reputation
Domain Age
Looks up when the sender domain was registered. Newly-registered domains carry elevated spam risk.
Content
Rspamd
Submits the full message to Rspamd — the dominant filter in self-hosted mail stacks — and maps the score to a verdict.
Content
SpamAssassin
Runs the message through SpamAssassin alongside Rspamd, so you see both perspectives in one run.
Authentication
BIMI
Checks whether the sender's domain publishes a BIMI record and validates any attached Mark Certificate (VMC).
What makes us different
A few things worth knowing about how the tool works.
Live SMTP transcript
Every command and reply streams to your browser as it happens, syntax-highlighted and linked to the relevant check. See exactly what happened at the protocol level.
Live session control
Accept, reject, drop or tarpit the connection mid-session without touching your server config. Useful for testing how sending systems handle various server responses.
Two spam engines, one run
Rspamd and SpamAssassin both run against your delivered message, giving you two independent spam filter scores in a single test.
Shareable results
Every result gets a stable URL you can share or revisit later. Results are kept for 30 days.