For enterprises, mergers and acquisitions (M&A) are about acceleration: expanding market share, entering new regions, and building scale. Yet with every acquisition comes the hidden cost of security complexity. Each acquired entity brings its own systems, tenants, and configurations, and many rely on outdated email gateways or unmanaged environments.

This creates a perfect storm of conditions that bad actors exploit. According to the FBI, over $2.7B in 2024 cybercrime losses came from business email compromise (BEC) alone. M&A periods are particularly vulnerable to threats because systems are in flux, communication channels are shifting, and oversight is divided. Attackers are quick to recognize and act on these gaps.

Enterprise acquisitions consistently introduce three email security challenges:

1. Too Many Tenants, Limited Visibility
   Every acquisition adds new Microsoft 365 or Google tenants, each with different rules, policies, and security baselines. For one global media company, merging 75 tenants across different gateways took over six months, delaying integration and leaving several subsidiaries exposed.
   
   

2. Unclear Inventory and Configuration Risk
   Before integration, teams often struggle to understand what they’ve acquired. Are all admin accounts protected by MFA? Are there risky OAuth apps connected to critical inboxes? A healthcare organization recently found that 14% of accounts in an acquired entity had no MFA, and several used legacy authentication methods that attackers could exploit.
   
   

3. Operational Drag and Licensing Friction
   Traditional gateways and manual licensing models make it difficult to onboard new users quickly. One global manufacturing firm discovered it was paying for overlapping SEG licenses across five acquired entities, all while new users remained unprotected.

These are not just IT headaches—they’re business risks that can delay synergies, erode trust, and diminish deal value.

Effective M&A security depends on early visibility and speed. The goal is to understand risk before integration begins, standardize controls during the transition, and maintain business continuity afterward.

In practice, the process follows these steps:

1. Establish Visibility Before the Deal Closes
   Security teams can connect to target environments in read-only mode to baseline risk without impacting mail flow or violating pre-close restrictions. Within hours, they can inventory users, apps, and vendors and quickly identify issues such as VIPs without MFA or unverified OAuth publishers.
   
   

2. Standardize Oversight Across Tenants
   A central management model enables consistent policy enforcement while preserving local team autonomy. This structure helps enterprises manage both Microsoft and Google tenants at once, unify reporting, and streamline response workflows.
   
   Recently, a large financial services company used this approach to oversee 12 newly acquired subsidiaries, cutting its email policy exceptions by 65% within a quarter.
   
   

3. Simplify Integration and Reduce Overhead
   Automation is key once the deal closes. Replacing legacy gateways, consolidating rules, and unifying phishing response can reduce operational drag significantly. Enterprises that adopt this model often see security coverage for new entities established within 4–6 weeks instead of months.

Abnormal applies these principles through its behavioral AI platform that connects directly to Microsoft 365 and Google Workspace, without mail routing or DNS changes.

This API-based approach allows enterprises to:

• Baseline user, app, and vendor risk pre-close

• Identify risky configurations with Security Posture Management

• Stop phishing and business email compromise on Day 1 with Inbound Email Security

• Streamline rule migration and reduce gateway costs

• Generate executive-ready risk reports through AI Data Analyst

Together, these capabilities allow enterprises to secure acquired environments quickly, without slowing integration or disrupting business operations.

Across large enterprises managing frequent acquisitions, Abnormal customers have reported:

• Integration completed in 4–6 weeks, compared to six months with legacy tools

• 95% reduction in manual email rule management, reclaiming an average of 96 SOC hours per week

• 42% lower licensing costs after replacing legacy SEG systems

• Faster Day 1 protection, with full coverage achieved using less than 10 hours of setup time

For one Fortune 500 manufacturer, Abnormal’s read-only visibility mode revealed 18 compromised inboxes in a target company before the acquisition closed, preventing potential financial and reputational loss.

Meanwhile, a global healthcare provider used Abnormal to consolidate five Microsoft 365 tenants and three legacy gateways, achieving full email protection across all subsidiaries in under six weeks.

M&A will always introduce complexity, but it doesn’t have to increase risk. The most effective security programs treat integration as a continuous process, starting with visibility, building toward standardization, and automating wherever possible.

Security leaders who take this approach can protect both the organization and the long-term value of the deal.

To see how Abnormal supports secure, low-friction enterprise integrations at scale, download the M&A brief below.