Microsoft is rolling out a new security capability designed to protect organizations from email bombing attacks, a growing cyberthreat that floods inboxes with massive volumes of messages to disrupt operations and hide legitimate communications.

The "Mail Bombing Detection" feature, part of Microsoft's Defender for Office 365 suite, will automatically identify and quarantine suspicious high-volume email campaigns without requiring additional configuration from IT security teams. The global deployment is scheduled to begin in late June 2025 and continue through July.

Email bombing represents a sophisticated attack strategy where cybercriminals overwhelm target mailboxes with excessive messages in short timeframes. These attacks serve dual purposes: degrading email system performance and burying critical communications under floods of junk mail.

"The deluge of junk emails can bury important messages, causing recipients to miss critical information or instructions," according to technical documentation describing the threat.

The new protection system employs machine learning algorithms to distinguish malicious bombing campaigns from legitimate high-volume communications like newsletters and marketing emails. The technology analyzes multiple factors including message velocity, sender reputation metrics, and content similarities between messages.

When suspicious patterns are detected, the system automatically routes flagged messages to users' junk folders while respecting existing safe sender configurations to avoid disrupting authorized communications.

Enhanced Security Operations

Security teams will gain comprehensive visibility into email bombing attempts through Microsoft's Defender portal interfaces, including Threat Explorer, Email Entity View, and Email Summary Panel. Organizations using programmatic monitoring can access detection data through Advanced Hunting queries using Kusto Query Language.

This integration ensures the new capability fits seamlessly into existing security workflows and reporting mechanisms.

Unlike many security updates that require manual configuration, Mail Bombing Detection will activate automatically across organizations using Defender for Office 365. Microsoft recommends that companies prepare by updating internal security documentation, reviewing junk folder policies, and briefing security operations teams on the new detection capabilities.

Organizations with compliance requirements should note that the feature modifies email classification processes and may affect audit logging for messages redirected to junk folders.

The launch addresses an increasingly prevalent attack vector in the evolving cyberthreat landscape, providing organizations with automated protection against email-based disruption campaigns.