What is a Secure Email Gateway? How They Work and Why They Aren’t Enough

A secure email gateway (SEG) is an email security solution that filters incoming and outgoing emails to detect suspicious and potentially malicious messages.

Many organizations use an SEG as part of their security mail system. Before emails reach employees' inboxes, they pass through the mail gateway, which scans for red flags indicating threats. It also monitors outgoing emails for sensitive information and blocks messages if risks are found.

Although SEGs are common email security gateway products, they often focus on traditional signs of gateway spam and phishing. This limits their ability to detect advanced social engineering attacks, which are growing in frequency and sophistication. Many organizations recognize these gaps.

So, why should you move beyond traditional SEGs? Continue reading to understand how SEGs work and why they may not fully protect your organization from today’s evolving email threats.

An SEG protects inboxes from suspicious emails. SEGs scan all incoming and outgoing emails, using a set of rules to determine whether an email is allowed to pass through the gateway to an inbox. They aim to filter out malicious emails and only deliver non-threatening emails.

SEGs detect emails with unwanted content like spam, phishing links, or malware. Once an SEG detects a potential email threat, it blocks the email from being sent and reaching the intended recipient. This reduces the odds that a company will fall victim to an email-based cyberattack because the email was never delivered in the first place.

Most SEGs provide a standard set of capabilities. Choosing an SEG with the right mix of features and proper configuration is critical to avoid security gaps. Here are the features of an SEG:

• Spam and Graymail Filtering: SEGs focus primarily on detecting and blocking spam emails. They look for common patterns in spam messages and then quarantine them. They may also include a feature for employees to mark an email as spam. These same features extend to graymail.

• Malicious Content Protection: Email gateways can detect certain elements of a phishing email, such as malicious links or attachments. However, sophisticated phishing attacks can pass these tests, evading SEG rules and delivering the email.

• Data Loss Prevention: Outgoing emails are also scanned with SEG. It looks for sensitive information in emails sent to an unauthorized recipient. DLP can help prevent intentional or accidental data leaks from employees.

• Email Encryption: Some SEGs offer end-to-end encryption to obfuscate sensitive messages and data.

SEGs are vital in defending organizations from diverse email threats. They combine advanced features to protect inboxes and networks. These combined capabilities allow SEGs to provide layered, adaptive protection, essential for modern email security challenges.

1. Sandboxing: Sandboxing isolates and executes suspicious email attachments or links in a controlled environment. This helps detect zero-day exploits and sophisticated malware by observing behavior without risking the actual network.

2. Content Disarm and Reconstruction (CDR): CDR proactively analyzes email content to remove potentially harmful code, then rebuilds a safe version for delivery. This approach ensures all email content is secure, going beyond traditional threat detection methods.

3. Data Loss Prevention (DLP): DLP scans outgoing emails for sensitive data like personal, financial, or proprietary information. When detected, emails can be blocked, quarantined, or encrypted to prevent unauthorized data exposure.

4. Anti-Phishing: Anti-phishing features protect against deceptive emails designed to steal credentials or financial details by:

• Scanning URLs against phishing databases

• Using machine learning to identify phishing traits in email content

• Alerting users or automatically quarantining suspicious messages

5. Post-Delivery Protection: Post-delivery protection addresses threats found after emails reach inboxes through:

• Retrospective scanning using updated threat intelligence

• Automated removal or quarantine of malicious emails

• User reporting tools that flag suspicious emails for analysis and action

It might seem like an SEG is enough to block email threats, but even the best SEGs have limitations. Attackers keep adapting, and many email security gateway products haven’t caught up.

While an SEG does a solid job filtering gateway spam and large-scale attacks, it often misses highly targeted phishing and social engineering emails.

The reason is that these sophisticated attacks don’t show the usual red flags, like suspicious attachments or spoofed domains, so the mail gateway lets them slip through to inboxes. That leaves your organization vulnerable to costly threats like business email compromise (BEC).

Plus, setting up an SEG means changing your MX record to redirect emails, which isn’t always quick or simple compared to API-based solutions.

SEGs frequently allow sophisticated social-engineering emails to pass unchecked.

Consider a supply chain compromise. In this cyberattack, a criminal compromises the account of a trusted vendor and sends an email about a payment transfer to one of your employees. The email contains no malicious links or attachments and is text-based only.

In a real case, an employee transferred $753,000 after receiving a message like the one above. Because the email contained no classic indicators of compromise, the SEG delivered it without hesitation.

A traditional SEG often allows suspicious emails to reach employees’ inboxes because they lack obvious red flags. These emails may come from trusted partners and contain no overt malware. However, modern email security solutions leveraging natural language processing (NLP) and behavioral models can detect unusual requests, such as an unexpected invoice with new deposit details, and mark them as suspicious.

BEC and account takeover threats continue to grow because many email gateways cannot detect socially engineered attacks. Organizations can augment or replace traditional SEGs with advanced email security gateway products that identify unusual email behavior in topic, tone, and sentiment.

API-Based Integrated Email Cloud Security (ICES) solutions provide deeper visibility into internal traffic, helping to prevent account takeovers, lateral phishing, and unwanted email content.

With cloud email providers like Google Workspace or Microsoft 365 and their built-in security, ICES can replace traditional mail gateways and offer more effective, comprehensive email protection.

Abnormal identifies modern threats that traditional SEGs miss. Most email gateways lack advanced AI and NLP capabilities to analyze subtle cues in emails and detect socially engineered attacks.

SEGs also have difficulty spotting suspicious internal emails, a gap that cloud-based security solutions are designed to address effectively.

Abnormal has the advanced email security tools you need to protect your organization from social engineering attacks. Some of our features include:

• Detects behavioral anomalies in emails by understanding relationships and context.

• API seamlessly integrates with email cloud providers like Microsoft 365 and Google Workspace.

• Additional visibility into internal emails for better threat detection.

• Evaluate vendor risk context for supply chain attacks.

• Monitors all emails, including those from trusted sources.

• Leverages cloud signals to search for compromised credentials, unusual sign-in events, and more.

There’s a reason why organizations are moving away from SEGs. Ready to enhance your email security and protect your organization from modern email threats? Get a demo to see how Abnormal can replace your SEG.