Mail tester

Checks SPF, DKIM (~30 common selectors), DMARC, MTA-STS, TLS-RPT, BIMI, MX reachability, and STARTTLS on the lowest-preference MX.

deepdig — network diagnostics

deepdig is a self-hostable, streaming network diagnostics toolbox: DNS, SSL/TLS, WHOIS, mail authentication (SPF/DKIM/DMARC/MTA-STS), HTTP headers, mail blacklists, IP info, and email-header analysis. The UI is a Vue SPA — if JavaScript is disabled, hit the JSON+SSE API directly:

curl -X POST https://deepdig.dev/api/v1/dns/check \
  -H 'Content-Type: application/json' \
  -d '{"domain":"example.com"}'
# returns { "session_id": "...", "sse_url": "/api/v1/dns/stream/..." }

curl -N https://deepdig.dev/api/v1/dns/stream/{session_id}

Full API in OpenAPI 3.1. Source: github.com/softplexity/deepdig.