The Problem SEG Solves

Nowadays, email is one of the most targeted places for scammers and hackers to find their victims. Statistics from Cisco state that 85% of email is spam, containing various malicious content like malware, phishing, ransomware, etc.

That is why email security is very crucial and vital in the enterprise email environment.
Cisco Secure Email Gateway (SEG), previously known as Cisco Email Security Appliance (ESA), is an appliance designed as a front-line defense for enterprise email infrastructure.

SEG Mail Flow Diagram 1: Cisco SEG as Mail Gatekeeper

What is Cisco SEG

Cisco SEG is an appliance that can be deployed either on-premise or in the cloud. If it is on-prem, it can be a physical or virtual appliance. This appliance sits in the mail flow path and inspects both inbound and outbound email. In other words, it is a Digital Gatekeeper that inspects and filters email before reaching the mail server.

Even if a company uses cloud email providers like Office 365 or Google Workspace, SEG can still be integrated to add advanced filtering and security layers.

SEG Role in Email Flow

During inbound mail flow, where most threats usually come from SEG scans every message. Depending on the result, it can drop, delay, or quarantine suspicious emails.

Meanwhile, during outbound mail flow, SEG helps prevent sensitive data leaks. If employees accidentally (or intentionally) send confidential information, SEG applies policies to block or encrypt the message, helping companies stay compliant.

SEG Key Components

Here are a few key components inside Cisco SEG that make everything work:

  • Listener

    • It is the entry point for every email that SEG receives (both inbound & outbound).
    • Listeners are always tied to interface IPs with port numbers (e.g., port 25, 587).

  • SMTP Routes

    • This is how SEG decides which route to take to deliver the email.
    • Think of it like a routing table in network devices.

  • Mail Processing Pipeline

    • This is where and how all the email processing happens.
    • This involves Mail Policies, Antivirus scanning, Spam filtering and other tasks.
    • Each message passes through these stages before delivery.

Why SEG is Still Relevant

All enterprises need to follow certain compliances, especially in compliance-heavy sectors like healthcare and finance. That’s why SEG is still needed today.

Besides that, hackers are always trying to find new ways to exploit vulnerabilities, so attacks are constantly evolving. Cisco SEG has its own internal research group, Cisco Talos, which provides threat intelligence to SEG when new attacks are discovered. This allows SEG to prevent new attacks early.

Also, SEG supports hybrid deployment, which fits most infrastructures, it can be on-prem, virtual or cloud-hosted by Cisco.