Secure Email Gateway (SEG)

Email remains the primary attack vector for cyber criminals targeting enterprise organizations worldwide. Recent research reveals that malicious email threats bypassing secure email gateways (SEGs) increased by over 105% in the past year, with analysts detecting a malicious email bypassing SEGs every minute of every day. This surge underscores the critical importance of understanding and implementing robust email security measures.

An email gateway is a type of email server that protects the internal email servers of organizations or users. This server acts as a gateway through which all incoming and outgoing emails pass. A secure email gateway is a device or software used for email monitoring that is used for sending and receiving.

Email gateway protection is designed to prevent unwanted emails while delivering legitimate ones. Unwanted messages include spam, phishing attacks, malware, or fraudulent content. Outgoing messages can be analyzed to prevent sensitive data from leaving the organization or to automatically encrypt emails that contain sensitive information. Modern SEGs deploy advanced technologies, including machine learning algorithms, signature analysis, and threat intelligence to identify and block sophisticated email threats. They examine email content, attachments, and embedded links in real-time before messages reach their intended recipients.

SEGs can be deployed as cloud-based services, on-premises appliances, or as hybrid solutions, depending on the organization’s requirements. They integrate seamlessly with popular email platforms, such as Microsoft 365 and Google Workspace, through API connections or DNS routing configurations. This flexibility allows businesses to maintain their existing email infrastructure while adding comprehensive security layers that adapt to evolving threat landscapes.

This multi-layered approach ensures that email threats encounter multiple barriers before reaching end-users, significantly reducing the risk of successful attacks.

Secure Email Gateways perform multiple interconnected security functions to create comprehensive email protection. These core capabilities work together to defend against the full spectrum of email-based threats while maintaining business productivity.

• Spam filtering: SEGs employ multiple techniques, including content analysis, sender reputation checks, and Bayesian filtering to identify and block unwanted messages before they reach user inboxes.
• Malware detection: Advanced scanning engines use signature-based detection, heuristic analysis, and behavioral monitoring to identify and block email-borne viruses and malicious software.
• Phishing protection: Anti-phishing mechanisms analyze email content for suspicious patterns, verify sender authenticity through protocols like DMARC, and use machine learning algorithms to detect sophisticated social engineering attempts.
• Business Email Compromise (BEC) detection: SEGs analyze sender behavior and communication patterns to identify fraudulent emails that impersonate executives or trusted business partners attempting to steal money or sensitive information.
• Content filtering: Systems scan email content to block offensive material, inappropriate communications, or messages that violate organizational policies and compliance requirements.
• Data Loss Prevention (DLP): DLP features scan outgoing emails for predefined patterns that match sensitive data, such as personal information, financial details, or proprietary content, to prevent unauthorized data leakage.
• Attachment and URL sandboxing: Suspicious email attachments and links are executed in controlled, isolated environments to observe their behavior and detect zero-day exploits without risking the actual network.
• Quarantine and user reporting: Suspicious messages are isolated in secure quarantine areas while users can report potentially malicious emails through integrated reporting mechanisms for further analysis.
• Encryption and archiving: SEGs automatically encrypt emails containing sensitive information and maintain secure archives of email communications to meet regulatory compliance and legal discovery requirements.

Secure Email Gateways defend against a comprehensive range of email-based threats that continue to evolve in sophistication and frequency.

Phishing & Spear Phishing

Cyber criminals send deceptive emails designed to steal credentials, personal information, or financial data by impersonating trusted entities. Current research shows that nearly 1.2% of all emails sent are malicious, resulting in 3.4 billion phishing emails circulating daily worldwide. Spear phishing targets specific individuals or organizations with highly personalized attacks that are particularly difficult to detect.

Business Email Compromise (BEC)

BEC attacks involve fraudsters impersonating executives, vendors, or business partners to manipulate employees into transferring funds or sharing sensitive information. These sophisticated social engineering attacks saw a 13% increase in February 2025 alone, with 40% of BEC emails now being generated by AI. The financial impact remains severe, with BEC accounting for billions in global losses annually.

Malware & Ransomware

Email attachments and malicious links serve as primary delivery mechanisms for malware that can encrypt files, steal data, or provide backdoor access to networks. Ransomware attacks occur at an alarming rate of 1.7 million incidents daily, with cyber criminals increasingly using email as their preferred infection vector. These attacks can paralyze business operations, resulting in significant financial and reputational damage.

Credential Harvesting

Attackers use fake login pages and social engineering tactics to collect usernames, passwords, and other authentication details from unsuspecting users. Nearly one-third of cyber-attacks in 2024 relied on abusing valid account credentials collected through harvesting techniques. Once obtained, these credentials enable attackers to bypass security measures and appear as legitimate users.

Spam and Graymail

Unwanted bulk emails consume network resources, reduce productivity, and can contain hidden malicious content or lead to more serious threats. Current data shows that 46% of all daily email traffic consists of spam, with 160 billion spam messages sent every day globally. Even legitimate but unwanted marketing emails can overwhelm inboxes and mask genuine security threats.

Data Exfiltration

Malicious actors attempt to steal sensitive corporate information, intellectual property, or customer data through email-based attacks and insider threats. SEGs monitor outbound communications to prevent unauthorized data transfers and ensure compliance with regulatory requirements. These protection mechanisms help organizations maintain data integrity and avoid costly breaches that can damage business relationships and regulatory standing.

Secure Email Gateways remain relevant, but their traditional capabilities must evolve to address modern threat landscapes. Current-generation SEGs are achieving detection rates exceeding 99.9% for conventional threats, yet they struggle with sophisticated attacks that bypass payload-based detection methods. The challenge lies not in abandoning SEGs but in recognizing their limitations against evolving attack vectors.

“For years now, secure email gateways (SEG) have been the go-to solution to stop them. They filter spam, phishing emails, and malware before they can get to users’ inboxes. But with more businesses adopting cloud-based email platforms—particularly Microsoft 365—alternative email security solutions have appeared on the market,” said Tim Bedard and Mark Harris of Proofpoint.

In turn, SEGs alone prove insufficient against today’s most dangerous threats, particularly credential phishing attacks that contain no technically malicious content. Research shows that 99% of email threats reaching corporate inboxes in 2024 were response-based social engineering attacks without malware payloads. GenAI-powered phishing campaigns now create error-free, highly personalized messages that appear legitimate to traditional rule-based detection systems. These attacks exploit the gap between what SEGs can detect and what attackers can craft.

Organizations increasingly adopt complementary security controls to address these blind spots. Behavioral analysis technologies establish communication baselines and flag deviations, reducing successful account takeover attacks. Identity threat protection, zero-trust frameworks, and post-delivery remediation capabilities work alongside SEGs to create layered defense strategies. This integrated approach recognizes that modern email security requires multiple detection methods working in concert rather than relying on any single solution.

Selecting the optimal Secure Email Gateway requires careful evaluation of several key factors that align with your organization’s specific security needs and operational requirements.

Deployment and Infrastructure Compatibility

Consider whether your organization prefers cloud-based, on-premises, or hybrid deployment models based on your IT resources and infrastructure capabilities. “For example, companies with multiple email environments, complex routing policies, or regulatory compliance needs often require the precision and control that a SEG provides,” says Andrew Goodman, Senior Manager of Product Marketing at Proofpoint.

Modern SEGs offer flexible deployment options, including traditional MX record-based routing, inline deployment through mail flow rules, and API-driven integration that works seamlessly with platforms like Microsoft 365 and Google Workspace. API-based deployment provides additional protection layers and advanced capabilities like social graph analysis and behavioral detection without requiring email routing changes.

Threat Coverage and Advanced Features

Evaluate the SEG’s effectiveness against your specific threat landscape, including spam filtering accuracy, malware detection capabilities, and advanced threat protection features. Organizations facing sophisticated attacks should prioritize solutions offering post-delivery remediation, threat intelligence integration, and behavioral analysis capabilities that can detect BEC and social engineering attacks. Consider whether the solution provides comprehensive outbound content control and data loss prevention features to protect sensitive information from leaving your organization.

Management and Integration Requirements

Assess the solution’s reporting capabilities, administrative usability, and integration potential with existing security tools like SIEM and SOAR platforms. Review compliance requirements specific to your industry and ensure the chosen SEG can meet regulatory standards while providing detailed logging and audit capabilities. Factor in the total cost of ownership, including licensing, training, and ongoing management resources required to maintain an optimal security posture.

Here are answers to common questions about Secure Email Gateways and their capabilities.

What’s the difference between a SEG and anti-spam?

While anti-spam solutions primarily focus on blocking unwanted bulk emails, SEGs provide comprehensive email security that includes spam filtering plus malware detection, phishing protection, BEC prevention, and data loss prevention. Think of anti-spam as a single security feature, while SEGs offer a complete suite of email protection capabilities. Modern SEGs use advanced technologies like machine learning and threat intelligence that extend far beyond traditional spam filtering.

Can SEGs block BEC and zero-day phishing?

Yes, modern SEGs can detect Business Email Compromise (BEC) attacks by analyzing sender behavior patterns and communication anomalies, though their effectiveness varies based on attack sophistication. Advanced SEGs use machine learning algorithms and threat intelligence to identify zero-day threats and novel attack methods that signature-based detection might miss. However, highly sophisticated impersonation techniques and carefully crafted social engineering attacks can still pose challenges for SEG detection capabilities.

Do SEGs inspect outbound mail, too?

Absolutely. SEGs analyze outgoing emails to prevent sensitive data from leaving the organization and can automatically encrypt messages containing confidential information. They enforce data loss prevention policies and help organizations maintain regulatory compliance by monitoring outbound communications. This bidirectional protection ensures that both incoming threats and outgoing data breaches are addressed.

What’s better: MX or API-based SEG?

Neither approach is definitively superior as each offers distinct advantages depending on organizational needs. MX-based SEGs provide pre-delivery threat filtering and work with any email infrastructure, while API-based email security solutions offer easier deployment and post-delivery remediation capabilities. Many organizations adopt hybrid approaches that combine both methods to maximize protection and minimize the limitations of either single approach.

Are SEGs effective for small businesses?

SEGs can be highly effective for small businesses, especially with cloud-based deployment options that reduce infrastructure requirements and management overhead. Small organizations often face the same email threats as larger enterprises but may lack dedicated security resources, making SEGs particularly valuable. The key is selecting an SEG solution that matches the organization’s technical capabilities and budget constraints while providing appropriate protection levels.

Secure Email Gateways remain a critical foundation in modern cybersecurity strategies, serving as the first line of defense in comprehensive layered email security architectures that protect against evolving threats. Proofpoint’s SEG technology is trusted by many of the world’s largest organizations to prevent advanced threats from reaching the inbox. With detection rates exceeding 99.99% and flexible deployment options including both traditional SEG and modern API-based approaches, Proofpoint delivers the integrated email security platform that Fortune 100 companies rely on to protect their people and data from sophisticated email-based attacks. Whether deployed as a standalone solution or part of a broader security ecosystem, Proofpoint’s advanced email security ensures your organization stays ahead of tomorrow’s threat landscape. Contact Proofpoint to learn more.