Adding a Secure Email Gateway

What a secure email gateway does

A Secure Email Gateway (SEG) sits in front of your mailboxes and screens inbound mail before it reaches anyone. It filters on message headers and content, checks links against reputation feeds, and strips or blocks risky attachments and active content such as macros. CISA describes this filtering as a core counter-phishing capability.

Why it's worth having

Email is a leading way attackers reach your people. The 2025 Verizon Data Breach Investigations Report found phishing involved in roughly one in six breaches, and email remains a common initial-access route. A gateway catches most of that automatically, before a person has to make the right call under pressure. CISA is clear that a gateway is one layer of defense, not a replacement for user awareness.

How to fix it

1. Turn on or upgrade filtering in your mail platform. Microsoft 365 (Defender for Office 365) and Google Workspace include gateway-style protection; dedicated SEG services add deeper scanning if you need it.
2. Configure the protective settings. Following CISA's recommendations, block active content and macros by default, enable URL reputation checks, and apply header and content filtering.
3. Pair it with quick user training. Anything that slips through still gets caught by a prepared team.

How to confirm it's fixed

Check your platform's quarantine or filter log - it should show messages being caught and categorized. Many providers also let you run a safe test message to confirm filtering is active. Ask your IT provider which gateway fits your current mail setup and how it is configured today.

Sources

• CISA - Enhanced Email and Web Security
• CISA - Counter-Phishing Recommendations
• Verizon 2025 Data Breach Investigations Report‍