Email Audit

Email Audit Sub-Skill

Purpose

Performs comprehensive email deliverability auditing for a domain. Checks DNS authentication records (SPF, DKIM, DMARC), infrastructure (MX, PTR, TLS), reputation (blacklists), and bulk sender compliance. Generates a health score (0-100) with prioritized fixes.

Input

• Domain name: e.g., rankenstein.cloud, example.com
• Optional: Email volume (triggers bulk sender compliance checks if 5,000+ emails/day)

Audit Categories

1. SPF Record (Weight: 10%)

What to check:

• SPF record exists at TXT <domain>
• Valid syntax: starts with v=spf1
• DNS lookup count (max 10, warn at 8+)
• Enforcement level: -all (pass), ~all (softfail), ?all (neutral), +all (fail)
• No multiple SPF records (causes validation failure)
• Includes are efficient and necessary

Commands:

dig txt <domain> +short | grep "v=spf1"
# or
python scripts/check_deliverability.py <domain> --spf

Scoring:

• Valid + hard fail (-all): 100 points
• Valid + soft fail (~all): 70 points
• Valid + neutral/pass all: 40 points
• Invalid syntax or 10+ lookups: 20 points
• Missing: 0 points

2. DKIM Record (Weight: 15%)

What to check:

• At least one valid DKIM record exists
• Key length: 2048-bit (required minimum per NIST), 1024-bit (legacy, upgrade recommended)
• Common selectors: google, default, selector1, selector2, k1, mandrill, dkim

Commands:

dig txt google._domainkey.<domain> +short
dig txt default._domainkey.<domain> +short
dig txt selector1._domainkey.<domain> +short
# Check common selectors

Note: DKIM selectors are not discoverable without prior knowledge. Check common ones and ask user if their email provider uses a specific selector.

Scoring:

• 2048-bit key found: 100 points
• 1024-bit key found: 70 points
• Invalid/weak key: 30 points
• Missing: 0 points

3. DMARC Policy (Weight: 15%)

What to check:

• DMARC record exists at TXT _dmarc.<domain>
• Policy level: p=reject (excellent), p=quarantine (good), p=none (monitoring)
• Aggregate reporting (rua=) tag present
• Forensic reporting (ruf=) tag present (optional)
• Alignment mode: aspf= (SPF) and adkim= (DKIM) - relaxed vs strict
• Percentage (pct=) should be 100 for full enforcement

Commands:

dig txt _dmarc.<domain> +short

Scoring:

• p=reject + rua + pct=100: 100 points
• p=quarantine + rua: 80 points
• p=none + rua: 40 points
• p=none without reporting: 20 points
• Missing: 0 points

4. MX Records (Weight: 10%)

What to check:

• Valid MX records exist
• MX hosts resolve to IP addresses
• Priority ordering is logical
• Mail provider identification (Google Workspace, Microsoft 365, custom)

Commands:

dig mx <domain> +short
dig a <mx-hostname> +short

Scoring:

• Valid + all hosts resolve + known provider: 100 points
• Valid + all hosts resolve: 80 points
• Valid but some hosts don't resolve: 40 points
• Missing or invalid: 0 points

5. Reverse DNS / PTR (Weight: 5%)

What to check:

• PTR records exist for MX server IPs
• PTR records match forward DNS (hostname matches)

Commands:

dig -x <mx-ip> +short

Scoring:

• All MX IPs have matching PTR: 100 points
• Partial PTR coverage: 50 points
• Missing PTR: 0 points

6. TLS/STARTTLS (Weight: 10%)

What to check:

• STARTTLS support on MX servers (port 25)
• TLS version (1.2+ recommended)

Commands:

openssl s_client -starttls smtp -connect <mx-hostname>:25 -brief

Note: This may require network access. If not available, note as "Unable to verify".

Scoring:

• TLS 1.2+ with STARTTLS: 100 points
• TLS 1.0/1.1 with STARTTLS: 60 points
• No STARTTLS: 0 points

7. Blacklist Check (Weight: 20%)

What to check:

• Domain and MX IP addresses against major blacklists:
  • Spamhaus (SBL, XBL, PBL)
  • Barracuda
  • SORBS
  • SpamCop
  • URIBL
  • Invaluement

Commands:

# Use checkdmarc library if available
python -c "import checkdmarc; print(checkdmarc.check_domains(['<domain>']))"

# Or manual checks
dig <ip>.zen.spamhaus.org +short
dig <ip>.b.barracudacentral.org +short

Scoring:

• Clean on all lists: 100 points
• Listed on 1 minor list: 50 points
• Listed on 1 major list (Spamhaus, Barracuda): 30 points
• Listed on 2+ major lists: 0 points

Critical: Any listing on major blacklists severely impacts deliverability.

8. Bulk Sender Compliance (Weight: 10%)

Applies to: Domains sending 5,000+ emails/day to Gmail, Yahoo, Microsoft recipients.

Requirements (Google/Yahoo/Microsoft 2024-2026 rules):

1. Both SPF AND DKIM must pass (not just one)
2. DMARC policy at minimum p=none with alignment
3. One-click unsubscribe header (RFC 8058: List-Unsubscribe-Post: One-Click)
4. Spam complaint rate under 0.3% (target under 0.1%)
5. Valid forward and reverse DNS (PTR records)
6. Honor unsubscribe within 2 business days
7. No impersonation of Gmail/Yahoo/Microsoft from headers
8. TLS connection for message transmission

Scoring:

• All 8 requirements met: 100 points
• 6-7 requirements met: 70 points
• 4-5 requirements met: 50 points
• Less than 4 met: 0 points

9. Additional Checks (Weight: 5%)

Bonus points for:

• BIMI record (Brand Indicators for Message Identification) at TXT default._bimi.<domain>
• MTA-STS policy at https://mta-sts.<domain>/.well-known/mta-sts.txt
• TLSRPT record at TXT _smtp._tls.<domain> (TLS reporting)
• Mail-from domain alignment (DKIM/SPF align with From: domain)

Commands:

dig txt default._bimi.<domain> +short
curl https://mta-sts.<domain>/.well-known/mta-sts.txt
dig txt _smtp._tls.<domain> +short

Scoring:

• Each bonus feature: +25 points (max 100)

Health Score Calculation

Formula:

Total Score = (SPF × 0.10) + (DKIM × 0.15) + (DMARC × 0.15) + (MX × 0.10) +
              (PTR × 0.05) + (TLS × 0.10) + (Blacklists × 0.20) +
              (Bulk Compliance × 0.10) + (Extras × 0.05)

Score Interpretation:

Workflow