API vs. SEG: Why the Future of Email Security is API-First

For nearly two decades, secure email gateways (SEGs) have been the default approach to protecting organizations from phishing and malicious email. They sit between the internet and the inbox, filtering messages before delivery. But the world of email has changed. Today, attackers are using increasingly sophisticated tactics that SEG architectures were never designed to stop.

A new approach has emerged: API-based email security. Instead of rerouting email traffic through a gateway, API-based solutions integrate directly with cloud email platforms like Microsoft 365 and Google Workspace. This shift is more than a technical detail. It represents a fundamental change in how organizations can protect their people, their data, and their trust.

The Problem with SEGs

SEGs were built for a different era of email. Their core model is traffic interception: inbound and outbound email flows are rerouted through the gateway, inspected, and then passed along to the mail server.

This approach has three major limitations:

1. Blind Spots in Modern Attacks
   Attackers increasingly use “payload-less” techniques like business email compromise (BEC), vendor impersonation, and social engineering. These emails often have no malicious link or attachment. Instead, they rely on intent and persuasion. SEG filtering, which is heavily pattern- and signature-based, struggles to catch them.

2. Time to Setup and Disconnect
   Deploying a SEG requires changing MX records and rerouting traffic through the gateway. That means downtime, added points of failure, and administrative overhead. And if an organization ever needs to disconnect or switch vendors, the process is equally disruptive and risky. For IT and security teams, this operational drag is one of the biggest strikes against the SEG model.

3. Lagging Behind the Cloud
   SEGs were created for on-premise servers. Cloud email platforms are dynamic, API-driven, and constantly updated. Bolt-on gateway architecture is a mismatch for the speed and agility of the cloud era.

How API-Based Security Works

API-based solutions connect directly to the mail platform via secure APIs. There’s no rerouting or traffic interception. Instead, the solution monitors email flow inside the tenant environment in real time.

This approach brings key advantages:

• Visibility Across the Entire Inbox
  Instead of only scanning messages at delivery, API solutions can evaluate the full context of a conversation, user history, and behavioral patterns. This makes it possible to catch attacks like BEC that rely on subtle impersonation or abnormal requests.

• Agentic Defense Against Links and Files
  Cambrient’s link and file agents actively follow redirects, attachments, and hidden behaviors inside emails. This is an active defense posture rather than passive filtering, surfacing threats that traditional SEG scanning would miss.

• Personalized to Each User
  Because API integrations see activity at the mailbox level, they can learn what “normal” looks like for each user. Anomalies stand out clearly, whether it’s a sudden attempt to reset a password or a message from a spoofed vendor domain.

• Simple Deployment
  Setup takes only a few clicks, with no MX record changes required. For administrators, that means minutes of configuration instead of days of traffic rerouting and risk. Disconnecting is just as fast, with no service disruption.

Why API Is the Future

Phishing is no longer about suspicious attachments or obvious spam. Attackers use social engineering, brand impersonation, and carefully crafted messages designed to slip past rule-based systems. SEGs were never designed to interpret meaning or intent.

API-based approaches are different. They allow solutions to analyze context, user behavior, and the actual intent behind a message. Combined with agentic techniques that follow links and files, this makes API solutions far better equipped to catch modern zero-day threats and business email compromise.

Even the major legacy players have noticed the shift. Barracuda, Proofpoint, Mimecast, Cisco, and Symantec are all attempting to pivot toward API-based offerings. But these companies are built on a SEG-first architecture, and their bolt-on API tools tend to underperform in speed, accuracy, and ease of deployment. Abnormal Security has made strides as a true API-first vendor, but beyond that, most attempts to rebrand SEG-era technology for a cloud-first world have fallen short.

Conclusion

The secure email gateway was once essential. But in 2025, it’s a relic. Email security now requires context, adaptability, and speed. API-based solutions deliver all three without the complexity and disruption of legacy gateways.

At Cambrient, we believe protection should be different by design. By integrating directly at the inbox level, analyzing intent, and deploying agents that act, we stop attacks that SEGs cannot. For organizations of any size, that means peace of mind and real security where it matters most: inside the inbox.