DNS & Email Security Posture Checker

Grade any domain's SPF, DKIM, DMARC, CAA and MX in seconds — free, passive, zero-install.

The Bug Circuit DNS & Email Security Posture Checker is a free, single-file command-line tool that tells you — in one command — how well a domain is protected against email spoofing and certificate abuse. Point it at a domain and it queries the live public DNS over DNS-over-HTTPS, inspects the records that matter for deliverability and anti-spoofing (A/AAAA, MX, SPF, DMARC, DKIM and CAA), and prints a clean, graded A-to-F report with the exact records you should publish to fix each gap.

It is deliberately passive and read-only. The tool makes the same ordinary DNS lookups any mail server makes to deliver a message — no host scanning, no port probing, no exploitation, no attack automation. That makes it safe to run against domains you own or are authorised to assess, and easy to drop into a CI pipeline or a periodic health check. Findings are prioritised (failures first, then warnings and informational notes), each with a plain-English explanation and a copy-pasteable fix, so non-specialists and seasoned admins alike can act on the results immediately.

Because it is pure Python 3 standard library — no pip installs, no external packages — it runs anywhere Python does on Windows, macOS and Linux. Output is colourised in your terminal and degrades gracefully to plain text for files and pipelines. A --json mode emits a structured report for dashboards and automation, --selectors lets you probe custom DKIM selectors, and meaningful exit codes let you gate builds on posture. It's a small, sharp, brand-quality utility from Bug Circuit that turns a fiddly manual DNS review into a five-second check.

How to use

• Install Python 3.8 or newer (it ships on most macOS/Linux systems; on Windows grab it from python.org). No other dependencies are needed.
• Download bugcircuit-dnsposture.py from Bug Circuit and open a terminal in the folder where you saved it.
• Run a check: python bugcircuit-dnsposture.py yourdomain.com (use python3 on macOS/Linux).
• Read the graded report — failures are listed first, each with a copy-pasteable DNS record to fix it.
• Publish the suggested SPF/DKIM/DMARC/CAA records at your DNS provider, then re-run to confirm the grade improves.
• For automation, add --json -o report.json, or probe a custom DKIM selector with --selectors yoursel.

Example commands

python bugcircuit-dnsposture.py example.com
python bugcircuit-dnsposture.py example.com example.org example.net
python bugcircuit-dnsposture.py example.com --selectors s1024,mysel
python bugcircuit-dnsposture.py --resolver google --json -o report.json example.com
python bugcircuit-dnsposture.py --help

Free · MIT licensed · Python 3.8+ · no dependencies · runs on Windows, macOS & Linux. A free tool from Bug Circuit.