Detecting Spearphishing With Email Gateway

Key Concepts

Spearphishing Characteristics

• Targeted recipients: Specific individuals, often executives or finance staff
• Researched pretexts: References to real projects, colleagues, or events
• Impersonation: Spoofs trusted senders (CEO, vendor, partner)
• Low volume: Few emails to avoid pattern-based detection
• Urgent tone: Creates pressure to act quickly

Gateway Detection Layers

1. Reputation filtering: IP/domain/URL reputation scoring
2. Authentication checks: SPF, DKIM, DMARC validation
3. Content analysis: NLP-based analysis of email body
4. Impersonation detection: Display name and domain similarity matching
5. URL analysis: Real-time URL detonation and redirect following
6. Attachment sandboxing: Behavioral analysis of attachments in isolated environments
7. Behavioral analytics: Anomaly detection in communication patterns

Workflow

Step 1: Configure Impersonation Protection

Microsoft Defender for Office 365:
  Security > Anti-phishing policies > Impersonation settings
  - Enable user impersonation protection for VIPs
  - Enable domain impersonation protection
  - Add protected users (CEO, CFO, HR Director)
  - Set action: Quarantine message

Proofpoint:
  Email Protection > Impostor Classifier
  - Enable display name spoofing detection
  - Configure lookalike domain detection
  - Set Impostor threshold sensitivity

Step 2: Configure URL Protection

• Enable Safe Links / URL rewriting
• Enable time-of-click URL detonation
• Block newly registered domains (< 30 days)
• Enable URL redirect chain following

Step 3: Configure Attachment Sandboxing

• Enable Safe Attachments / attachment sandboxing
• Configure dynamic delivery (deliver body, hold attachments)
• Set sandbox detonation timeout to 60+ seconds
• Block macro-enabled Office documents from external senders

Step 4: Create Custom Detection Rules

Use the scripts/process.py to analyze email gateway logs, identify spearphishing patterns, and generate custom detection rules.

Step 5: Configure Alert and Response Actions

• Real-time alerts for impersonation attempts
• Automatic quarantine for high-confidence detections
• User notification with safety tips
• Integration with SIEM for correlation

Tools & Resources

• Microsoft Defender for Office 365: https://security.microsoft.com
• Proofpoint Email Protection: https://www.proofpoint.com/us/products/email-security
• Mimecast Email Security: https://www.mimecast.com/products/email-security/
• Barracuda Email Protection: https://www.barracuda.com/products/email-protection

Validation

• Impersonation protection correctly identifies spoofed VIP display names
• URL detonation catches malicious links in test phishing emails
• Attachment sandboxing detects weaponized documents
• Custom rules trigger on known spearphishing patterns
• SIEM integration receives gateway alerts