An email gateway is a perimeter system that filters, inspects, and routes inbound and outbound mail before it reaches user mailboxes or leaves the organization. It usually sits between the internet and the internal messaging environment, handling spam filtering, malware scanning, policy enforcement, encryption, and logging.
In cyber security, email gateways matter because they process large volumes of untrusted content from outside the network. That makes them high-value targets: a flaw in mail parsing, attachment handling, or message inspection can let an attacker bypass defenses, deliver phishing or malware, or even execute code on the gateway itself. Defenders use these systems to block malicious messages and to detect suspicious patterns in mail traffic, while attackers try to abuse the same trust boundary to reach users or gain a foothold on a perimeter appliance. Strong patching, log review, and version management are essential because a compromised gateway can expose both communication flow and security visibility.