Email is still the easiest way into your business. Phishing, BEC, and stealthy malware keep slipping past legacy defenses especially now that most companies run on Microsoft 365 or Google Workspace. For years, Secure Email Gateways (SEGs) were the default. But the center of gravity has shifted to cloud-native, API-based security that works inside your tenant instead of in front of it.
This guide explains the difference in plain terms, where SEGs fall short, and why API-level protection (like MailArmor) has become the practical choice for cloud email.
Bottom line: SEGs protect the perimeter. API security protects the mailbox.
How Threats Evolved and Why That Matters
Trusted clouds as bait: Links hosted on reputable services and QR codes often slide past perimeter filters.
Account takeover and insider risk: Compromised accounts launch attacks from inside your organization where a gateway has little visibility.
Beyond email: Files and messages in Teams, Slack, OneDrive, and Drive create new paths for attackers.
Faster mutation: Polymorphic phishing and dynamic payloads outpace static rules.
Perimeter-only defenses were built for a world of on-prem servers and predictable traffic. That world is gone.
Why API-Based Email Security Wins in Cloud Environments
Cloud-native rollout
Connect securely to Microsoft 365 or Google Workspace. No MX changes, no mail-flow surgery, no downtime.
360° visibility
See inbound, outbound, and lateral communications. Scan historical mail to find dormant threats. Understand user behavior and conversation context not just headers and links.
Behavior and intent detection
Go beyond signatures to catch social engineering cues (e.g., urgent payment requests, supplier fraud, impersonation patterns) that typical filters miss.
Post-delivery control
If a campaign is detected after the fact, automatically retract or neutralize the message across all affected inboxes something gateways can’t do.
Protection that extends past email
Monitor risky links/files in Microsoft Teams, Slack, OneDrive, and Google Drive to reduce cross-channel exposure.
Where Traditional SEGs Struggle
Operational drag: MX/routing complexity introduces risk and slows projects.
Blind spots: Limited view of internal mail and anything that happens after delivery.
Rule fatigue: Constant rule tuning and false-positive management.
SaaS gap: Minimal coverage for modern collaboration tools.
Latency and resilience: Extra hops can add delay and single points of failure.
SEGs aren’t “bad” they’re just optimized for yesterday’s perimeter.
The MailArmor Approach (API-First)
MailArmor is built for cloud tenants from the start integrating via Microsoft Graph and Google APIs to protect users without interrupting mail flow.
MailArmor pairs real-time threat intel with mailbox-level context to spot phishing, BEC, ransomware links, and insider risks without slowing down your users or touching MX records.
When API-Based Email Security Is the Right Call
Choose an API-first platform if you:
- Run Microsoft 365 or Google Workspace (single-tenant or multi-tenant).
- Want zero-downtime deployment and no MX changes.
- Need post-delivery remediation and BEC/ATO detection.
- Care about visibility across internal emails and collaboration tools.
- Prefer lower maintenance over constant rule wrangling.
Working with legacy Exchange? A transitional setup (SEG + API) can bridge the gap until you complete your cloud migration.
Verdict - Explore MailArmor’s API-first approach
The perimeter isn’t where your risk lives anymore the mailbox is. API-based email security is the practical way to defend modern, cloud-connected organizations. If you’re still relying solely on a gateway, you’re defending yesterday’s attack surface.
With MailArmor, teams get: continuous monitoring, intent-aware detection, rapid post-delivery fixes, and coverage that follows the work from email to collaboration tools. Book a technical walkthrough and register our waitlist to get early access.