Email is still the most targeted attack surface in cybersecurity — and traditional defenses are struggling to keep up. Rule-based secure email gateways, built for a world of spam and simple phishing, are increasingly blind to the sophisticated, AI-generated social engineering attacks that now dominate the threat landscape.
Abnormal Security was built specifically to solve this problem. Unlike legacy tools that scan for known bad patterns, Abnormal uses behavioral AI to model what normal looks like for every user, vendor, and relationship in an organization — and flags anything that deviates from that baseline. The result is a platform capable of catching attacks that no rule-based system could detect.
This guide explains what Abnormal Security is, how it works, what threats it stops, and whether it’s the right fit for your organization.
The Origins and Mission Behind Abnormal Security
Abnormal Security was founded in 2019 in San Francisco by Evan Reiser and Sanjay Jeyakumar, both former Twitter engineers with deep backgrounds in machine learning and large-scale behavioral data systems. The company’s founding thesis was simple but bold: the only way to reliably stop socially engineered email attacks is to understand human behavior at scale — not just inspect email content for known threat signatures.
The company’s growth has been remarkable. By 2024, Abnormal had reached over $200 million in annual recurring revenue and closed a $250 million Series D funding round that valued the company at $5.1 billion. It serves more than 2,800 customers worldwide, including 20% of the Fortune 500, across industries ranging from financial services and healthcare to manufacturing and retail.
In December 2024, Abnormal was named a Leader in the inaugural Gartner Magic Quadrant for Email Security Platforms — and was placed furthest right on the Completeness of Vision axis among all 14 evaluated vendors. That recognition was repeated in the 2025 edition, making Abnormal a back-to-back Gartner Leader.
How Abnormal Security’s Behavioral AI Engine Actually Works
At the core of the Abnormal platform is what the company calls its Abnormal Behavior Technology (ABX). Rather than relying on threat signatures, blocklists, or manually configured rules, ABX builds a dynamic behavioral model of every identity in an organization — employees, executives, vendors, and external senders.
The platform ingests data through a direct API integration with Microsoft 365 or Google Workspace. This API-based architecture means Abnormal processes emails after they have passed through native filters — acting as a second, far more intelligent layer of defense rather than replacing the email flow entirely.
Here is what the behavioral model analyzes for each message:
- • Identity and relationship context: Has this sender emailed this recipient before? Is the domain new or recently registered? Does the sender’s communication pattern match historical behavior?
- • Tone and linguistic signals: Does the message carry unusual urgency, financial pressure, or secrecy cues that are inconsistent with the sender’s normal communication style?
- • Content and intent: What is the email asking the recipient to do? Does the request match the sender’s known role and the recipient’s job function?
- • Timing and behavioral anomalies: Is this email sent at an unusual hour? Does the volume of outbound email from this account spike suddenly?
By combining these signals across thousands of data points per message, Abnormal can detect payloadless attacks — messages with no malicious links or attachments — that are completely invisible to traditional secure email gateways (SEGs).
What Makes Behavioral AI Different from Traditional Email Security
Traditional secure email gateways operate primarily on pattern matching: they scan incoming messages against databases of known malicious URLs, attachment signatures, and sender blacklists. This works reasonably well for mass spam campaigns but fails almost entirely against targeted, well-crafted social engineering attacks — because those attacks contain no detectable malicious payload. Behavioral AI flips this model: instead of asking ‘does this match a known threat?’, it asks ‘does this deviate from known-good behavior?’ That distinction is what allows Abnormal to catch threats that others miss.
The Full Spectrum of Threats Abnormal Security Stops
Abnormal Security is designed to address the full range of modern email-based threats, including many that fall outside what legacy tools can handle.
• Business Email Compromise (BEC): BEC attacks involve impersonating executives or trusted partners to trick employees into transferring funds or sharing sensitive information. The FBI estimated BEC caused over $2.9 billion in losses in 2023 alone. Abnormal’s behavioral models detect the impersonation even when no malicious link or file is present.
• Credential Phishing: Emails that direct users to fake login pages to steal usernames and passwords. Abnormal analyzes both the email context and any embedded links for behavioral anomalies — detecting phishing even when the destination URL has never been seen before.
• Account Takeover (ATO): When a legitimate employee account is compromised, attackers use it to send internal phishing emails or initiate fraudulent wire transfers. Abnormal monitors post-login behavior and can automatically disable a compromised account within milliseconds of detecting anomalous activity.
• QR Code Phishing (Quishing): Abnormal’s H1 2024 Threat Report revealed that C-suite executives receive QR code phishing attacks at 42 times the rate of average employees. Construction and engineering firms experience quishing at 19 times the rate of other industries. Abnormal detects these by analyzing the email context surrounding QR codes, not just the codes themselves.
• Supply Chain Compromise: Attackers target vendors and suppliers to send fraudulent invoices or intercept payments. Abnormal’s VendorBase uses federated behavioral intelligence to identify when a known vendor’s communication pattern has been compromised.
• Graymail and Productivity Threats: Beyond security threats, Abnormal also filters unwanted marketing and newsletter emails on a per-user basis, using individual behavioral preferences rather than blanket rules.
Key Products and Platform Capabilities
Abnormal Security is not a single product but a platform of integrated modules, each addressing a different dimension of email and cloud security.
• Inbound Email Security: The core product — AI-powered analysis of every incoming message for the full range of attack types listed above.
• Account Takeover Protection: Continuous monitoring of user behavior across email and connected SaaS platforms to detect and remediate compromised accounts automatically.
• Security Posture Management (SPM): Identifies misconfigurations in Microsoft 365 environments — such as risky third-party app permissions or dormant admin accounts — and provides prioritized remediation guidance.
• AI Security Mailbox: An AI-powered abuse mailbox that automatically triages user-reported suspicious emails, analyzes them, and sends personalized feedback to the reporting employee. This dramatically reduces the manual workload on SOC analysts.
• AI Phishing Coach: Automatically converts real-world attack attempts into targeted phishing simulations and delivers just-in-time coaching to employees — no manual simulation campaign configuration required.
• Search & Respond: An investigation tool that allows security teams to search across all mailboxes by sender, subject, attack type, or campaign and take bulk remediation actions.
Deployment: API-Based Setup in Under 15 Minutes
One of Abnormal Security’s most frequently cited advantages is its deployment speed. Unlike traditional secure email gateways that require MX record changes and complex configuration, Abnormal deploys through a direct API integration with Microsoft 365 or Google Workspace.
According to verified customer reviews on Gartner Peer Insights, many enterprise customers complete initial setup in under 15 minutes. There are no rules to configure, no policies to define, and no email flow changes to manage. The platform begins building its behavioral baseline immediately upon connection and typically reaches full detection efficacy within a few days as it learns the organization’s communication patterns.
This low-friction deployment model is a significant operational advantage for resource-constrained security teams. Abnormal reports that 70% of customers are able to eliminate redundant third-party secure email gateways after deploying — reducing overall email security spend while improving protection.
Abnormal Security and Microsoft 365: A Natural Pairing
Abnormal is particularly well-suited to organizations running Microsoft 365. It integrates natively via Microsoft’s Graph API, ingesting behavioral signals from Exchange Online, SharePoint, OneDrive, and Teams. This unified data feed allows Abnormal to correlate email behavior with activity across the broader Microsoft 365 environment — for example, flagging a suspicious email in the context of an unusual SharePoint file download that occurred in the same session.
Real-World Performance: What the Data Shows
Abnormal Security’s effectiveness claims are supported by several publicly available data points. The company’s most recent threat report documented a 50% year-over-year increase in overall advanced email threats across its customer base, alongside a 350% increase in MFA-bypass attacks using compromised file-sharing tools like Dropbox and SharePoint.
Legacy secure email gateways, by contrast, saw a 250% increase in the attacks they missed during the same period — a gap that underscores the limitations of signature-based approaches against modern AI-generated threats.
On Gartner Peer Insights, Abnormal holds a 4.8 out of 5 average rating from 263 verified reviews as of late 2024, with a 99% willingness-to-recommend rating — one of the highest in the email security category.
How Abnormal Security Compares to Traditional Secure Email Gateways
Organizations evaluating Abnormal Security often ask how it compares to established SEG vendors like Proofpoint, Mimecast, or Microsoft Defender for Office 365.
• vs. Proofpoint and Mimecast: These are mature, rule-based platforms with strong threat intelligence feeds and compliance tooling. They excel at blocking known threats at scale. Abnormal focuses specifically on the gap these platforms leave — unknown, payloadless, and behavioral attacks. Many organizations deploy Abnormal alongside or as a replacement for these tools.
• vs. Microsoft Defender for Office 365: Microsoft’s native protection is included with many M365 licenses but relies heavily on Microsoft’s own threat intelligence. Abnormal’s independent behavioral AI layer provides a measurably different detection approach, catching threats that Defender misses — as evidenced by the large number of customers who run both.
Abnormal’s positioning is not as an either/or replacement for all existing tools, but rather as the behavioral AI layer that catches what everything else misses.
Who Should Consider Abnormal Security?
Abnormal Security is an enterprise-grade platform best suited to mid-market and large enterprise organizations, particularly those running Microsoft 365 or Google Workspace at scale. It is especially valuable for:
• Organizations with high BEC exposure: Financial services, legal, real estate, and healthcare firms that handle frequent wire transfers or sensitive data are prime BEC targets.
• Security teams overwhelmed by manual triage: The AI Security Mailbox and automated remediation capabilities directly reduce analyst workload.
• Companies that have experienced account takeovers: Abnormal’s ATO detection and automated response capabilities are among the most sophisticated available.
• Enterprises consolidating their security stack: 70% of customers reduce or eliminate their legacy SEG after deploying Abnormal, streamlining both operations and spend.
Final Verdict: Why Abnormal Security Stands Out in a Crowded Market
Abnormal Security has earned its position at the forefront of email security not through marketing claims but through measurable results. Its behavioral AI approach addresses a genuine gap in the market — the growing population of sophisticated, AI-generated, payloadless email attacks that defeat traditional defenses.
With back-to-back Gartner Magic Quadrant Leader recognition, a 99% customer recommendation rate, and proven performance at Fortune 500 scale, Abnormal Security represents one of the most compelling options in enterprise email protection today. For organizations still relying solely on legacy SEGs or native Microsoft protection, it offers a meaningful and operationally lightweight upgrade.
FAQs
Is Abnormal Security a replacement for Microsoft Defender?
Not exactly a replacement — more of a complement. Many organizations run Abnormal Security alongside Microsoft Defender for Office 365. Abnormal’s behavioral AI catches threats that Defender’s rule-based system misses, particularly payloadless social engineering attacks and account takeovers.
How long does Abnormal Security take to set up?
Deployment takes as little as 15 minutes via API integration with Microsoft 365 or Google Workspace. No MX record changes, no policy configuration, and no disruption to email flow are required. The platform begins learning behavioral baselines immediately upon connection.
Does Abnormal Security work for small businesses?
Abnormal Security is primarily designed for mid-market and enterprise customers. Its platform supports deployments from 100 to 600,000 mailboxes. Smaller organizations may find the pricing structure better suited to enterprise budgets, though the company does serve organizations across a wide range of sizes.
What is the difference between Abnormal Security and a secure email gateway?
A secure email gateway (SEG) sits in the email delivery path and filters messages based on known threat signatures, blocklists, and rules. Abnormal Security uses behavioral AI to analyze every email against a baseline of normal behavior — catching socially engineered attacks that contain no detectable malicious payload and would pass through any rule-based filter.
How does Abnormal Security handle false positives?
Abnormal’s behavioral model is designed to minimize false positives by understanding relationship context before flagging a message. Legitimate emails from known senders that match historical patterns are not flagged. Users can report missed attacks directly, and the system remediates at campaign level — removing all related emails from all mailboxes automatically.
