Implementing Mimecast Targeted Attack Protection

Implementing Mimecast Targeted Attack Protection

Overview

Mimecast Targeted Threat Protection (TTP) is a suite of advanced email security services designed to protect against sophisticated phishing, spearphishing, and targeted attacks. TTP consists of four core modules: URL Protect (real-time URL rewriting and click-time analysis), Attachment Protect (sandbox detonation of suspicious attachments), Impersonation Protect (BEC and whaling detection), and Internal Email Protect (scanning internal/outbound email for threats). As of November 2025, Mimecast enabled URL Pre-Delivery Action with Hold setting for all customers by default.

When to Use

• When deploying or configuring implementing mimecast targeted attack protection capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Common Misconfigurations & Verification

• URL Protect in rewrite-only mode: without Pre-Delivery Action set to "Hold", a URL weaponized between delivery and click can still reach the user - enable pre-delivery hold (default since Nov 2025) and verify it on existing policies.
• Impersonation at Hit 3 for everyone: the default 3-indicator threshold misses single-signal VIP attacks - create a separate Hit 1 VIP definition for CEO/CFO/finance and keep Hit 3 for the general population.
• Attachment Protect "Safe File" only: static safe-file conversion alone misses behavior-based payloads - use Dynamic Configuration (full sandbox) for unknown senders and allow timeout for complex files (up to ~7 min).
• Internal Email Protect not enabled: without journaling from M365/Workspace, lateral phishing from a compromised internal account is invisible - enable IEP URL and attachment scanning.
• Over-broad permitted senders / managed URLs: blanket bypasses defeat URL and impersonation scanning - scope exceptions to specific automated systems and mailing lists.
• Verification: pilot on 50-100 users first; send a test URL, an EICAR/test attachment, and a VIP-impersonation BEC; confirm the URL is rewritten and blocked at click, the attachment is sandboxed within SLA, the impersonation is quarantined, and pre-delivery hold catches a weaponized URL before inbox.

Prerequisites

• Mimecast Email Security license with TTP add-on
• Administrative access to Mimecast Administration Console
• Microsoft 365 or Google Workspace environment
• MX records configured to route through Mimecast
• Understanding of email authentication (SPF, DKIM, DMARC)

Key Concepts

TTP Module Overview

Impersonation Protection Scenarios

• Hit 3 (Default): Flags emails matching 3+ impersonation indicators
• Hit 1 (VIP): Flags emails matching 1+ indicator for designated VIP users
• Key identifiers: display name similarity, domain similarity, reply-to mismatch, newly registered domains

URL Protect Modes

• Rewrite: URLs rewritten to route through Mimecast proxy at click time
• Pre-Delivery Action (Hold): URLs checked before message delivery; held if suspicious
• Pre-Delivery Action (None): URLs checked pre-delivery but not held

Workflow

Step 1: Configure URL Protect Policy

• Navigate to Administration > Gateway > Policies > Targeted Threat Protection - URL Protect
• Create URL Protect definition with rewriting enabled for inbound messages
• Enable URL Pre-Delivery Action set to "Hold" for maximum protection
• Configure scan mode: aggressive for high-risk users, moderate for general population
• Set action for malicious URLs: block page with user notification
• Enable URL logging for all click events

Step 2: Configure Attachment Protect Policy

• Navigate to Administration > Gateway > Policies > Targeted Threat Protection - Attachment Protect
• Create Attachment Protect definition for inbound email
• Select sandbox mode: "Safe File" (converts to safe format) or "Dynamic Configuration" (full sandbox)
• Configure attachment types to scan: executables, Office documents, PDFs, archives
• Set timeout for sandbox analysis (default: up to 7 minutes for complex files)
• Enable pre-emptive sandboxing for attachments from unknown senders

Step 3: Configure Impersonation Protect

• Create Default Impersonation Protect Definition (Hit 3) for all inbound email
• Create VIP Impersonation Protect Definition (Hit 1) for executive protection
• Build VIP list: CEO, CFO, CTO, board members, finance leadership
• Configure detection identifiers: display name, domain similarity, newly observed sender
• Set actions: quarantine high-confidence impersonation, tag moderate confidence
• Enable end-user warning banners for flagged messages

Step 4: Enable Internal Email Protect

• Configure journaling from Microsoft 365/Google Workspace to Mimecast
• Enable URL scanning for internal emails
• Enable attachment scanning for internal emails
• Configure alerts for internal account compromise indicators
• Set up detection for internal phishing (compromised account sending malware)

Step 5: Create Test Group and Validate

• Create pilot group of 50-100 users across departments
• Apply TTP policies to pilot group first
• Send test emails with known-safe test URLs and EICAR test files
• Verify URL rewriting, attachment sandboxing, and impersonation detection
• Monitor false positive rate for 1-2 weeks before organization-wide deployment

Step 6: Deploy Organization-Wide and Tune

• Extend TTP policies to all users
• Monitor Mimecast Threat Dashboard for detection metrics
• Review and whitelist legitimate applications triggering false positives
• Tune impersonation sensitivity based on false positive feedback
• Configure exception policies for automated systems and mailing lists

Tools & Resources

• Mimecast Administration Console: Policy configuration and management
• Mimecast Threat Dashboard: Real-time threat visibility and analytics
• Mimecast Awareness Training: Integrated security awareness platform
• Mimecast API: Programmatic access to logs and threat data
• Message Center: Quarantine management for admins and users

Validation

• URL Protect rewrites URLs in test messages and blocks known-malicious at click
• Attachment Protect sandboxes test file and returns verdict within SLA
• Impersonation Protect flags test BEC email impersonating VIP
• Internal Email Protect detects test lateral phishing scenario
• Pre-delivery hold catches weaponized URL before reaching inbox
• False positive rate below organizational threshold after tuning