woman using secure email gateway to secure emails in office
101 Guide
7 min

What Is A Secure Email Gateway (SEG)?

With billions of emails sent daily, the risk of cyber threats is a major concern in the business world. This is where secure email gateways (SEGs) become crucial. Acting as security guards for your digital communications, SEGs protect your email data as it enters or leaves your email system.

Secure email gateways can scan inbound emails for malicious content, ensuring they are safe to open.

SEGs can also take actions on outbound emails like scanning, encrypting, or adding authentication measures to prevent data loss through email interception or human error.

How Does A Secure Email Gateway Work?

Secure email gateways provide security for multiple users, using features such as content filtering, malware protection, and encryption to prevent email-based threats.

SEGs operate differently based on their features and focus on either inbound or outbound threats.

Inbound vs outbound secure email gateways

Inbound Secure Email Gateways

Inbound secure email gateways focus on preventing threats from incoming emails by following these steps:

1. Email Traffic Is Intercepted: The gateway operates at the network's edge, intercepting messages before they reach the recipient's inbox.

2. Email Content Is Scanned: The gateway scans email content, including URLs and attachments, for malicious elements using techniques like signature-based detection, machine learning, or reputation analysis.

3. Threats Are Identified and Blocked: If threats such as malware, phishing attempts, or spam are detected, the gateway can delete the message, quarantine it, or send it to the spam folder.

4. Safe Emails Are Delivered: Emails deemed safe are delivered to the recipient's inbox, ensuring only legitimate emails pass through.

Outbound Secure Email Gateways

For secure email gateways focusing on preventing outbound threats, the process involves encryption and recipient authentication:

1. Email Message Creation: Users create and attach documents to emails as usual. If the email meets certain criteria, such as specific phrases in the subject line, it will be marked for secure sending.

2. Authentication Challenge: Before sending, the sender can set an authentication challenge for the recipient, such as answering a question or receiving a passcode.

3. Server Checks and Encryption: The email undergoes DLP, AV, and server-side signature checks before being encrypted with two keys.

4. Key Management: One key is sent to the recipient, while the other remains in a secure vault until the recipient passes the authentication challenge, ensuring security even if the email is intercepted.

Discover more about how email encryption gateways function.

Exploring The Common Features Of A Secure Email Gateway

A secure email gateway uses various techniques and tools to determine email safety, whether sending or receiving emails.

Inbound Email Gateway Features

Gateways protecting against inbound threats typically include the following features:

Spam Filtering

Spam filtering identifies and removes malicious or unwanted emails from incoming traffic, preventing spam and phishing emails from reaching users' inboxes.

Phishing is the most reported method of cyber attack

A SEG filters spam using methods such as:

Content Filtering: Analyses email content for keywords associated with spam.

Blacklisting: Blocks emails from known spam sources or domains.

Reputation-Based Filtering: Blocks emails from senders with poor reputations based on past behaviour.

Virus And Malware Screening

Virus and malware screening involves identifying and blocking email attachments and links containing malicious content.

The gateway scans all email attachments and links for malware, quarantining or blocking emails if threats are detected, and sometimes notifying the sender.

Colleagues looking at secure email together

Machine Learning

Machine learning uses AI to improve email filtering and threat detection by recognising patterns associated with malicious emails.

Examples include:

Content Analysis: Identifying spam or phishing-related keywords or phrases.

Behavioural Analysis: Analysing email traffic patterns to detect suspicious activity.

Outbound Secure Email Gateway Features

Gateways focusing on protecting outbound emails often include:

Data Loss Prevention (DLP)

Data Loss Prevention (DLP) helps prevent the disclosure of sensitive information by analysing outbound emails and attachments for financial data or intellectual property.

Depending on the findings, the DLP system can:

  • Block the email from being sent;
  • Notify the sender and/or recipient;
  • Quarantine the email for further review.

Advanced systems can remove or replace sensitive information before sending.

How does data loss prevention work


Secure email gateways with archiving features help organisations meet legal and regulatory requirements by retaining a copy of all emails.

Archives support e-discovery requests and help businesses stay compliant with industry regulations.


Email encryption scrambles email contents to prevent unauthorised access.

Critical for outbound email security, some gateways automatically encrypt emails with sensitive content.

Make sure messages are encrypted

To set up email encryption, your mail server must route outbound emails through the gateway. Encryption can be triggered by:

  • Detecting an attachment;
  • Recipient's email domain;
  • Keywords in the subject line;
  • A specific X-header;
  • Emails marked as confidential.

Email Revoke

Email revoke allows the sender to block access to a message after sending, even if it has been opened.

This feature is useful for correcting human errors, such as sending an email to the wrong person, and helps prevent unintended data access.

Many email clients offer limited recall functions, but a secure email gateway provides broader email revoke capabilities, reducing data breach risks.

Leader looking at a desktop computer in office

Audit Trails

Secure email gateways assist in maintaining regulatory compliance by logging interactions between senders and recipients.

Gateway audit functions record opens, downloads, and revoke actions, allowing senders to monitor email status and receive notifications of recipient interactions.

Email audit trails are crucial for compliance, especially in financial services and other highly regulated sectors.

Security Phrases

Security phrases prompt users to send emails securely when certain words are detected in the message content.

Gateways with this feature scan for phrases associated with sensitive information, such as:

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

This feature acts as a safety net for users who might forget to secure emails manually.

Why Is A Secure Email Gateway Needed?

Email is the most used tool for businesses and consumers, with an estimated 347 billion messages sent daily.

Unfortunately, email was not built with security in mind and poses significant risks.

Secure email gateways help prevent several key risks:


Phishing involves a malicious party pretending to be a legitimate source to trick recipients into clicking a link, leading to a fraudulent website or malware download.

Studies, like the one from IBM, show that 41% of cyber-attacks use phishing.

Training colleague on secure email gateway functions

Phishers may pose as entities like Royal Mail or your bank, aiming to extract sensitive information or install malware.

Secure email gateways scan email content for malicious links to prevent phishing emails from reaching inboxes.


Email interception occurs when a third party gains unauthorised access to an email in transit or on a server, potentially stealing sensitive data.

Gateways counteract this with end-to-end encryption and recipient authentication, ensuring emails are secure even if intercepted.

Human Error

Human error, such as sending emails to the wrong person, is a significant risk, especially with sensitive information.

Research indicates that over 50% of consumers have shared personal data via email, with a quarter sending it to the wrong recipient. Notably, 90% of data breaches are due to human error.

Secure email gateways mitigate these risks through authentication and email revoke features, ensuring only intended recipients access messages.

Recipient authentication can involve sending a one-time code, answering a security question, or ID verification.

Read enterprise secure email

Who Is A Secure Email Gateway Designed For?

Secure email gateways are ideal for organisations using email regularly and looking to secure their communications data.

This is particularly crucial for those handling sensitive data in regulated industries such as financial services, legal, government agencies, educational institutions, and non-profits.

What Are The Benefits Of A Secure Email Gateway For Businesses?

Beyond enhanced email security, there are several business benefits to using secure email gateways:

Compliance With Regulation

Many industries must adhere to strict data protection regulations, like the UK GDPR, which requires secure email practices.

The Information Commissioner’s Office (ICO) advises using encryption to protect personal data transmitted via email.

Increased Trust And Credibility

Protecting customer data builds trust and loyalty, while data breaches can significantly damage a company's reputation.

Research shows that 33% of businesses lose customers, and 34% face reputational damage following a cyber incident.

Reduced Risk Of Financial Loss

Cyber attacks can be costly, with IBM estimating the global average cost of a data breach at $4.35 million.

Businesses face losses from customer churn and potential ICO fines, which can reach up to £17.5 million or 4% of annual turnover, whichever is higher.

What Should You Look For In A Secure Email Gateway?

Office workers encrypting their sensitive emails

When choosing a gateway, consider the following factors:


Gateways can be deployed on-premise or in the cloud. The best choice depends on your budget, infrastructure, and resources.


For organisations sending large volumes of emails, look for a gateway that supports bulk delivery and automates secure messaging.


Consider secure email gateway integrations that simplify deployment, such as M365 and Unipass Identity.


Security solutions should be user-friendly for both senders and recipients, ensuring smooth workflows.

Secure Email Gateways

A secure email gateway adds a layer of protection against email threats, inspecting inbound and outbound emails for malware, phishing attempts, and spam.

By identifying and blocking potentially dangerous emails, a secure email gateway helps prevent security breaches, data loss, and cyber attacks that could compromise an organisation's systems or sensitive information.

Deliver sensitive information securely with Mailock


Number of Emails Sent and Received Daily Worldwide, Statista, 2023

IBM X-Force Threat Intelligence Report, IBM, 2023

Psychology of Human Error and Security Breaches, CISO Mag, 2024

Impact of Cyber Incidents on Business, RedSeal, 2019

Reviewed By:

Sam Kendall, 14.06.24

Sabrina McClune, 14.06.24


Originally posted on 19 04 23
Last updated on June 18, 2024

Posted by: Sabrina McClune

Sabrina McClune is an expert researcher with an MA in Digital Marketing. She was a finalist in the Women In Tech Awards 2022. Sabrina has worked extensively with B2B technology companies conducting and compiling thorough academically driven research to produce online and offline media. She loves to read fantasy novels and collect special edition books.

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