Detecting Spearphishing with Email Gateway Skill

Detecting Spearphishing with Email Gateway

Overview

Spearphishing targets specific individuals using personalized, researched content that bypasses generic spam filters. Email security gateways (SEGs) like Microsoft Defender for Office 365, Proofpoint, Mimecast, and Barracuda provide advanced detection capabilities including behavioral analysis, URL detonation, attachment sandboxing, and impersonation detection. This skill covers configuring these gateways to detect and block targeted phishing attacks.

When to Use

When investigating security incidents that require detecting spearphishing with email gateway
When building detection rules or threat hunting queries for this domain
When SOC analysts need structured procedures for this analysis type
When validating security monitoring coverage for related attack techniques

Prerequisites

Access to email security gateway admin console
Understanding of email flow architecture (MX records, transport rules)
Familiarity with SPF/DKIM/DMARC authentication
Knowledge of common spearphishing techniques and pretexts

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

Reputation filtering: IP/domain/URL reputation scoring
Authentication checks: SPF, DKIM, DMARC validation
Content analysis: NLP-based analysis of email body
Impersonation detection: Display name and domain similarity matching
URL analysis: Real-time URL detonation and redirect following
Attachment sandboxing: Behavioral analysis of attachments in isolated environments
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

Agent Skills: Detecting Spearphishing with Email Gateway

Install this agent skill to your local

Skill Files