API Email Security vs Secure Email Gateway

Are your email security filters protecting your employees from malicious threats? 

The data might surprise you. 

Research conducted by Check Point* found that 68% of malicious attacks are delivered through email, with 22% of all malicious email attachments hidden in PDFs. 

Without the right email security solutions, your inbox becomes more vulnerable to malicious emails and attachments, especially with the use of AI, where attackers can generate phishing content at scale and continuously vary payload delivery to evade detection.

But before you can take any preventive measures, it’s essential to have a deeper understanding of the primary email security solutions. 

In this blog, we’ll break down the key differences between a secure email gateway (SEG) and API email security, including best practices, and how to determine which approach is right for your organization. Let’s dive right in. 

What Are Secure Email Gateways?

A secure email gateway (SEG) acts as a defense point for inbound and outbound email traffic by analyzing message content, malicious attachments, and suspicious URLs using signature-based detection, behavioral analysis, sandboxing, and machine learning (ML) to block threats before they reach recipients. 

SEGs help identify and prevent malicious attachments, business email compromise (BEC), graymail, spear phishing, and other phishing threats from bypassing spam filters through continuous monitoring, pattern recognition, and policy enforcement. Emails are inspected through multiple detection layers, including signature-based scanning, behavioral analysis, and machine learning classifiers, and are either blocked or quarantined before delivery.

Secure email gateways filter harmful content and isolate suspicious emails in separate quarantine environments for further analysis and to verify sender authenticity. Anomaly detection models and machine learning engines help identify emerging attack patterns that might otherwise bypass traditional security controls. SEG capabilities also include data loss protection (DLP), anti-phishing features to prevent domain spoofing, and content disarm and reconstruction (CDR), which removes potentially malicious code from attachments while preserving file usability. 

Configuring a SEG begins with updating the organization’s DNS MX records to route all inbound email through the gateway to the mail server before delivery. Once routing is in place, emails should be tested and validated to ensure correct mail flow, proper TLS handshake negotiation, and that only legitimate messages are being delivered. 

What Is API-Based Email Security?

API-based email security integrates with cloud-based email platforms such as Microsoft 365 and Google Workspace using native APIs. 

They differ from secure email gateways in that they do not sit inline in the mail flow or require DNS MX record changes, but instead operate directly within the email environment to continuously scan and monitor mailboxes both before and after delivery. 

No DNS modifications or infrastructure changes required. From an operational standpoint, API-based email security wins on speed of deployment and business continuity. 

Secure email gateways often require complex mail routing changes and third-party specialized outsourced services to implement and maintain, driving up cost and operational overhead, whereas API-based solutions can be deployed in minutes using native platform integrations. 

Secure Email Gateways and API-Based Email Security

We’re going to explore the advantages and disadvantages of both email security options and what organizations should consider before making a decision. 

Here is a side-by-side comparison of both email security solutions. 

Secure Email Gateways	API-Based Email Security
Complex configuration, maintenance, and deployment	Can be deployed in minutes
Requires continuous updating of MX records	API-native. No mail routing changes required
Prone to latency due to inline scanning	Post delivery protection
Limited ability to integrate with existing security tools, such as SIEM	Integrates with SIEM and SOAR platforms
High false positives. Legitimate emails may be inadvertently flagged as suspicious, potentially disrupting operations	Better user experience
Limited to signature-based detection and heuristics	More enhanced threat detection with AI and ML capabilities
Ineffective in detecting polymorphic malware and zero-day exploits	Mailbox-level visibility
Difficulty adapting to emerging threats	Cost efficient

Email security lies at the core of any successful MSP program. The biggest threats to an organization come in the form of a seemingly “harmless” file attachment that a spam filter missed because it was obfuscated or delivered via zero-day malware campaigns. Research taken from the Email Threat Trends Report 2025: Q3** found that out of 1.8 billion emails processed, there was a 13% increase in malicious emails YoY, and nearly 150k newly discovered malicious files. 

It only takes a single malicious file that somehow lands in the CFO’s inbox to cause a massive breach if the right email security protocols are not in place. 

Choosing Between Secure Email Gateways and API Email Security

So, which option should you choose?

For SMBs that don’t have a team of dedicated network engineers on staff to integrate and maintain a SEG, going the path of native API-based email security is often the more practical and lower-risk option. 

Organizations that are fully in the cloud benefit more from API-based solutions, while hybrid or on-prem deployments might see better results from SEGs due to their ability to enforce inline malware blocking and policies at the perimeter. 

Shifting the existing email infrastructure for a large-scale enterprise on-prem isn’t exactly that simple because the traffic must be rerouted through the gateway, TLS certificates may need to be reconfigured, and connectors updated. The smallest misconfiguration can introduce mail flow disruptions and delivery delays. 

All of this translates into additional risk, increased expenses, and internal friction among teams. 

The choice is quite clear.  

Securing Your Inbox with Guardz

Guardz helps prevent phishing attacks and malicious emails with inline API-based email protection directly into the Guardz unified cybersecurity platform. MSPs benefit from having Check Point’s Harmony Email Security (formerly Avanan) to help secure clients’ inboxes. 

Guardz API-based email security integration deploys seamlessly via Microsoft 365 or Google Workspace APIs, without any agents or MX record changes for continuous mailbox scanning on delivery. Guardz provides advanced payload detection, contextual analysis, and deep inspection of embedded links and attachments, utilizing AI and threat intelligence to detect hidden malware and suspicious emails. 

Keep malicious emails out of your inbox with Guardz.

Get started today

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FAQs about Outsourcing SEGs vs API-based Email Security

Are secure email gateways still effective against modern phishing attacks? 

Secure email gateways are no longer effective due to the sophistication of phishing attacks. 

Can API-based email security replace a secure email gateway?

 Yes. API-based email security can provide strong post-delivery detection, mailbox-level visibility, and automated remediation without changing mail flow

How do secure email gateways impact email delivery and performance? 

Secure email gateways sit inline, so all inbound and outbound messages must pass through them for inspection. This can introduce additional latency, delivery delays, and operational disruptions. 

Sources:

*[email protected] & [email protected]. (2025, April 2). The Weaponization of PDFs : 68% of Cyber attacks begin in your inbox, with 22% of these hiding in PDFs. Check Point Blog. https://blog.checkpoint.com/research/the-weaponization-of-pdfs-68-of-cyberattacks-begin-in-your-inbox-with-22-of-these-hiding-in-pdfs/
**VIPRE Security Group. (2025, December 12). VIPRE’s Email Threat Trends Report: Q3 2025 – VIPRE. VIPRE. https://vipre.com/resources/q3-2025-email-threat-report/