Secure Email Gateway.

A perimeter or cloud service that filters inbound and outbound email for spam, phishing, malware, data leakage, and policy violations before it reaches user mailboxes. It belongs to the Network Security category of cybersecurity.

A perimeter or cloud service that filters inbound and outbound email for spam, phishing, malware, data leakage, and policy violations before it reaches user mailboxes.

A Secure Email Gateway (SEG) sits between the public internet and an organization's mailboxes, often as a cloud service such as Microsoft Defender for Office 365, Proofpoint, Mimecast, Cisco Secure Email, or Google Workspace's advanced protection. It enforces SPF, DKIM, DMARC, MTA-STS, and STARTTLS, scans messages with anti-malware engines, sandboxing, URL rewriting, and impersonation detection, and applies content rules and DLP for outbound mail. SEGs integrate with directory services, MFA-enabled admin consoles, and SIEM/SOAR for response. Newer Integrated Cloud Email Security (ICES) products complement SEGs with API-based, behavior-driven detection inside Microsoft 365 and Google Workspace, focused on business email compromise and lateral phishing.

Defences for Secure Email Gateway typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: SEG, Email Security Gateway, Mail Security Gateway.