Tools

Free, no sign-up. Each one answers a different question about your mail.

Domain check
Everything a domain publishes for email: SPF, DKIM, DMARC, BIMI, MTA-STS, TLS-RPT and DNS security, graded on one Report Card with the fixes in order.
Live send test
Send one real message to us and see what a receiving server saw: its SPF, DKIM and DMARC verdicts, the DKIM selector you actually sign with, and the reverse DNS of the IP you send from.
Header checker
Paste the raw headers of any email and see how SPF, DKIM and DMARC evaluated, and how that lines up with what the From domain publishes.
SPF sender test
Would mail from this server pass SPF? Give an IP and a MAIL FROM address and get the verdict a strict receiver reaches, plus the exact term in the record that decides it.

See what a full SPF breakdown looks like on a big setup: nasa.gov's SPF, lookup by lookup →