email-audit（电子邮件审核）

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

Step 1: Gather Domain Information

Ask user for:

• Domain name to audit
• Approximate email volume (to trigger bulk sender checks)
• Known DKIM selector (if not using common ones)

Step 2: Parallel Delegation

Spawn these agents in parallel for faster auditing:

Agent 1: email-deliverability

Check DNS authentication records for <domain>:
- SPF record validation
- DKIM record discovery (selectors: google, default, selector1, selector2, k1)
- DMARC policy analysis
- MX record validation
- PTR/reverse DNS check

Return JSON with pass/fail status and raw records.

Agent 2: email-compliance

Check bulk sender compliance for <domain>:
- Verify both SPF and DKIM pass
- Check DMARC alignment
- Note TLS support
- Check for List-Unsubscribe headers (if sample email provided)

Return compliance checklist with met/not met status.

Agent 3: email-reputation (if tools available)

Check reputation for <domain>:
- Blacklist status (Spamhaus, Barracuda, SORBS, SpamCop)
- Historical deliverability issues
- Spam complaint rate (if available)

Return list of blacklist hits and reputation score.

Step 3: Aggregate Results

Collect results from all agents and calculate weighted health score.

Step 4: Generate Prioritized Fix List

Categorize issues by priority:

Critical (Fix Immediately):

• Blacklist listings
• Missing SPF/DKIM/DMARC
• Invalid DNS records
• MX records not resolving

High (Fix Within 1 Week):

• Weak SPF enforcement (~all instead of -all)
• 1024-bit DKIM keys (upgrade to 2048-bit)
• DMARC policy p=none (upgrade to p=quarantine or p=reject)
• Missing PTR records

Medium (Fix Within 1 Month):

• Missing aggregate reporting (rua tag)
• No TLS/STARTTLS support
• SPF approaching 10 DNS lookup limit
• Missing bonus features (BIMI, MTA-STS, TLSRPT)

Step 5: Generate DNS Record Recommendations

Provide exact DNS records to add/update with copy-paste ready values.

Output Format

Structure the audit report as:

1. Header: ## Email Deliverability Audit: [domain] with date, health score, rating
2. Authentication table: SPF/DKIM/DMARC with status, score, raw records
3. Infrastructure table: MX/PTR/TLS with status, score, provider detection
4. Reputation: Blacklist status across Spamhaus, Barracuda, SORBS, SpamCop
5. Bulk Sender Compliance: 8-requirement checklist (Google/Yahoo/Microsoft rules)
6. Bonus Features: BIMI, MTA-STS, TLSRPT, Mail-from alignment
7. Prioritized Fix List: Critical/High/Medium with impact, fix steps, DNS records
8. DNS Records to Add: Copy-paste ready TXT/MX records
9. Next Steps: Immediate, this week, this month, monitoring, re-audit

Use score weights from Health Score Calculation section. Use status badges: ✅ PASS, ⚠️ WARN, ❌ FAIL.

Tools

Run python scripts/check_deliverability.py <domain> --json for automated DNS checks.

Manual DNS commands (used in audit categories above):

• SPF: dig txt <domain> +short
• DKIM: dig txt <selector>._domainkey.<domain> +short
• DMARC: dig txt _dmarc.<domain> +short
• MX: dig mx <domain> +short
• PTR: dig -x <ip> +short
• TLS: openssl s_client -starttls smtp -connect <mx-hostname>:25 -brief

Quality Gates

Before delivering audit results:

1. All critical checks completed (SPF, DKIM, DMARC, MX, Blacklists)
2. Health score calculated with breakdown by category
3. Prioritized fix list generated with specific action steps
4. DNS records provided in copy-paste ready format
5. Score interpretation explained with next steps

Error Handling

If DNS queries fail:

• Note as "Unable to verify" in audit report
• Provide manual check instructions
• Suggest alternative DNS servers (8.8.8.8, 1.1.1.1)

If DKIM selector unknown:

• Check common selectors (google, default, selector1, selector2)
• Ask user for their email provider's DKIM selector
• Note as "DKIM selector not found - requires manual verification"

If no MX records found:

• Critical failure - domain cannot receive email
• Check if domain uses mail forwarding (Cloudflare, etc.)
• Provide setup instructions for email hosting

References

Load on demand:

• references/deliverability-rules.md - Scoring thresholds and compliance rules
• references/mcp-integration.md - Provider-specific setup and DNS configuration
• references/compliance.md - Compliance rules and regulatory requirements

Success Criteria

Audit is successful when:

• Health score accurately reflects deliverability state
• All critical issues identified with clear severity levels
• User receives actionable DNS records to implement
• Fix priority aligns with business impact
• Re-audit timeframe provided based on score