What Is a Secure Email Gateway (SEG)?

With billions of emails sent every day, organisations need a reliable way to filter, monitor, and protect email traffic. A secure email gateway (SEG) sits between senders and recipients to help block threats on the way in and add safeguards on the way out.

Email remains one of the most common routes for malware, phishing, and accidental data leakage.

Secure email gateways can scan inbound emails for malicious content before they reach the inbox.

They can also apply controls to outbound emails, including scanning, encryption, and recipient authentication, to reduce the risk of interception and human error.

How Does a Secure Email Gateway Work?

Secure email gateways protect multiple users by using features such as content filtering, malware protection, and encryption to block email-based threats.

They work in different ways based on their features, focusing on inbound or outbound security.

Inbound Secure Email Gateways

Inbound gateways target threats coming in via your emails by following these steps:

1. Email Traffic Is Intercepted: The gateway sits at the network’s edge, stopping messages before they reach your inbox.

2. Email Content Is Scanned: It checks the body, URLs, and attachments for malicious content using signature-based detection, machine learning, or reputation tools.

3. Threats Are Identified and Blocked: If malware, phishing attempts, or spam are found, the gateway can delete the message, quarantine it, or mark it as spam.

4. Safe Emails Are Delivered: Messages that pass inspection are sent to the inbox. Only valid messages get through.

Outbound Secure Email Gateways

Gateways that focus on outbound threats use email encryption and recipient authentication, often in these ways:

1. Email Message Creation: Users write emails and attach documents; if certain criteria are met, like specific words in the subject line, the email is tagged for secure sending.

2. Authentication Challenge: Before sending, the sender can require the recipient to answer a question or use a passcode.

3. Server Checks and Encryption: The email goes through DLP, antivirus, and signature checks before it's encrypted with two keys.

4. Key Management: One key is sent to the recipient, while the other stays in a secure vault until the recipient passes the authentication step - this keeps the email safe even if it's intercepted.

Learn more about outbound email encryption gateways.

Exploring the Common Features of a Secure Email Gateway

A secure email gateway uses different methods to test whether emails are safe, whether you're sending or receiving them.

Inbound Email Gateway Features

Gateways designed to stop inbound threats often include:

Spam Filtering

Spam filtering spots and removes malicious or unwanted emails, stopping spam and phishing from reaching users.

A SEG filters spam using methods like:

• Content Filtering: Checks for spam keywords.
• Blacklisting: Blocks emails from known spam sources.
• Reputation-Based Filtering: Blocks emails from senders with bad reputations.

Virus and Malware Screening

Virus and malware screening looks for harmful files or links in your emails.

The gateway scans all attachments and links. If it finds threats, it blocks or quarantines them and might notify the sender.

Machine Learning

Machine learning uses AI to improve threat detection by recognising patterns linked to harmful messages.

Some examples include:

• Content Analysis: Spots spam or phishing-related words.
• Behavioural Analysis: Monitors email traffic patterns for suspicious activity.

Outbound Secure Email Gateway Features

Gateways aiming to target outbound emails might include:

Data Loss Prevention (DLP)

Data Loss Prevention (DLP) helps stop private information from leaving your organisation.

It checks outbound messages and attachments for financial data or intellectual property.

Based on its findings, DLP can:

• Block the email.
• Notify the sender or recipient.
• Quarantine the email for extra checks.

More advanced systems can remove or replace sensitive content before sending.

Archiving

Secure email gateways with archiving features help organisations stay compliant by saving a copy of all emails.

Archives support e-discovery and confirm that businesses follow regulations.

Encryption

Email encryption scrambles messages so unauthorised people can't read them.

It's essential for outbound email security.

Some gateways encrypt sensitive emails automatically.

To set up encryption, your mail server sends outbound emails through the gateway.

Encryption can be triggered by:

• Detecting an attachment.
• The recipient’s domain.
• Keywords in the subject line.
• A certain X-header.
• Emails marked as confidential.

Email Revoke

Email revoke lets you block someone from seeing an email after it’s sent, even if they opened it once.

This is useful for fixing human errors like sending an email to the wrong person.

It helps prevent people from reading data they shouldn’t have.

Some email apps offer basic recall options, but a secure email gateway goes further with revoke capabilities, which lowers the risk of data breaches.

Audit Trails

Secure email gateways help with regulatory compliance by logging what happens between senders and recipients.

They record opens, downloads, and revokes, so senders can track email status and get notified when recipients interact with messages.

These audit trails support compliance expectations, especially in financial services and other highly regulated sectors.

Security Phrases

Security phrases prompt users to send emails in a secure way if the system finds certain words in the content.

Gateways that use this feature look for words tied to sensitive information, like:

• ‘Attachment’
• ‘Confidential’
• ‘Invoice’
• ‘Payslip’
• ‘Account’

This helps users who might forget to secure an email themselves.

Why Is a Secure Email Gateway Needed?

"All organisations face the challenge of balancing strong security with a smooth user experience.

A secure gateway helps businesses avoid critical mistakes by checking and safeguarding each email."

Paul Holland, Founder and CEO, Beyond Encryption (Mailock)

Email is widely used by businesses and consumers. The Radicati Group estimates that around 392.5 billion emails will be sent and received worldwide each day in 2026.

Sadly, email was not built with security in mind and carries serious risks.

Secure email gateways help block several key risks:

Phishing

Phishing happens when a criminal pretends to be a trusted source to trick users into clicking a link that leads to fake websites or malware.

Research says 41% of cyber attacks start with phishing.

Scammers might act like Royal Mail or a bank to steal sensitive info or install malware.

Secure email gateways scan for bad links so phishing emails don’t end up in users’ inboxes.

Interception

Email interception is when an unauthorised third party reads an email in transit or on a server, putting private data at risk.

Outbound secure email gateways can fight this by combining end-to-end encryption and recipient authentication.

This can keep messages safe even if someone intercepts them in transit.

Human Error

Sending an email to the wrong person is a big problem, especially if it includes confidential info.

Our research shows 50% of consumers have sent personal data via email, with one in four sending it to the wrong contact.

Secure email gateways can cut these risks with authentication and email revoke, making sure only the right people can read your messages.

Recipient authentication might use a one-time code, a security question, or ID verification to verify a message reaches the right person.

Who Is a Secure Email Gateway Designed For?

A secure email gateway suits organisations that email often and need to protect sensitive communications.

It's especially important for those handling sensitive data in fields like financial services, legal, government, education, and non-profits.

Learn more about financial services email compliance.

What Are the Benefits of a Secure Email Gateway for Businesses?

Aside from stronger email security, a secure email gateway can support several business benefits:

Compliance with Regulation

Many industries must follow strict data protection regulations, such as the UK GDPR, which calls for secure email practices.

The Information Commissioner’s Office recommends using encryption to protect personal data sent by email.

Increased Trust and Credibility

Protecting customer data builds loyalty, while data breaches can seriously harm a company’s reputation.

Many organisations lose business and brand value after a cyber attack.

Reduced Risk of Financial Loss

Cyber attacks can be expensive.

IBM's 2025 Cost of a Data Breach Report puts the global average cost of a data breach at USD 4.44 million.

Businesses risk losing customers and may face fines of up to 4% of their annual turnover.

What Should You Look for in a Secure Email Gateway?

When choosing a gateway, you’ll want to consider:

Deployment

You can deploy gateways on-premise or in the cloud, depending on your budget, infrastructure, and resources.

Automation

If you send lots of emails, look for a gateway that supports bulk delivery and automates secure messaging.

Integrations

Look for integrations that make setup, sending secure emails, or the recipient experience easier, such as M365 and Unipass ID.

Ease of Use

Security solutions should be easy to use for both senders and recipients, supporting smooth workflows.

Securing Email to Protect Your Organisation

A secure email gateway offers a protective layer against threats, checking inbound and outbound emails for malware, phishing, and spam.

By spotting and blocking dangerous messages, a secure email gateway helps stop security breaches, data loss, and cyber attacks that could harm an organisation’s systems or sensitive data.

FAQs

What Is a Secure Email Gateway?

A secure email gateway filters and monitors messages to block threats like malware, phishing, and spam.

It adds safeguards for both incoming and outgoing emails to keep sensitive data safe.

Can a Secure Email Gateway Prevent Human Error?

It can't remove human mistakes completely but features like recipient authentication, email revoke, and prompts for sensitive data cut down on accidental leaks.

How Does Encryption Work with a Secure Email Gateway?

When the gateway sees certain triggers, it encrypts your email so only authorised recipients can read it, even if the message is intercepted in transit.

References

Email Statistics Report, 2024-2028 - Executive Summary, The Radicati Group, 2024

IBM X-Force Threat Intelligence, IBM, 2023

Cost of a Data Breach Report, IBM, 2025

Encryption Guidance, Information Commissioner's Office, 2024

Reviewed by

Sam Kendall, 02.06.26

Sabrina McClune, 23.12.2024

This content is for general information only and is not legal advice.