Revolutionizing Email Security: The Evolution of EnGarde Secure Linux to EnGarde Cloud Email Security

There’s a story behind every company and every product. At Guardian Digital, this story began with the inception of a foundationally secure, highly customizable server-only Linux distribution, EnGarde Secure Linux, in 2001.

The first Linux distro designed solely for security, EnGarde Secure Linux took an OS already renowned for its security and stability and made it notably more secure through the implementation of SELinux by default, along with other unique security features. EnGarde Secure Linux user and Cyber Defense Group CEO Lou Rabon attests, "Many years ago, I had the privilege of working with EnGarde as a newbie security professional.  It was the only secure-out-of-the-box *nix distro I could confidently use for my clients.  EnGarde was ahead of its time, and it's part of the DNA of the cybersecurity industry."

Despite the success and impact of EnGarde Secure Linux during its decade as a standalone product, at Guardian Digital, we’ve always acknowledged that digital security is anything but stagnant, and defenses must evolve to meet organizations’ ever-changing security needs. With the proliferation of cloud email and its central role in over 90% of modern cyberattacks, we recognized the need for superior email protection to make email safe for business. We also saw the potential in EnGarde Secure Linux to provide an inherently secure and resilient foundation for developing business email security solutions. Today, Guardian Digital EnGarde Cloud Email Security, built on the foundation of EnGarde Secure Linux, provides exceptionally secure, highly customizable email protection to organizations of all sizes worldwide.

Let’s look at how our approach to digital security has evolved over the years and the notable benefits your business will experience by securing its email infrastructure with EnGarde Cloud Email Security.

EnGarde Secure Linux: A Linux Distro Ahead of Its Time

EnGarde Secure Linux was an open-source server-only Linux distribution developed by Guardian Digital in 2001. EnGarde incorporated open-source tools such as Postfix, BIND, and the LAMP stack. The platform included services for web hosting, DNS, email, among other services. In 2005, SELinux was incorporated into the platform by default, making EnGarde Secure Linux one of the earliest distributions to include SELinux for complete server implementations and one of the first Linux server platforms designed solely for security. EnGarde improved the security of existing versions of Linux in critical areas with advanced forms of data integrity management and assurance, a complete suite of e-business services, intrusion alert capabilities, improved authentication and access control utilizing strong cryptography, and complete SSL secure web-based administration capabilities. Users could configure these services through the command line or remotely manage them through WebTool, the platform's browser-based interface. 

There were twenty-one releases of EnGarde Secure Linux since September 2005, before we shifted our focus exclusively to business email security. Guardian Digital CEO Dave Wreski explains the transition and how EnGarde Secure Linux has provided a secure, resilient foundation for the business email security services Guardian Digital provides today: 

“EnGarde Secure Linux was battle-tested and shown to protect against evolving threats, proving it could provide a secure foundation for applications, including cloud email security solutions. We have built our EnGarde Cloud Email Security on this inherently secure foundation, and everything we learned during the ten years it was a standalone product. In this sense, EnGarde Secure Linux has been retired, but its legacy lives on!”

Guardian Digital EnGarde Cloud Email Security: Comprehensive Business Email Protection Built on EnGarde Secure Linux

Adequate email security is contingent upon defense in depth. A comprehensive approach is required to fortify email against sophisticated modern exploits. We recognize this and have engineered our landmark business email security solution, EnGarde Cloud Email Security, with the type of modern, multi-layered design required to combat today’s advanced threats. The various layers of security that comprise EnGarde work harmoniously to detect and block threats in real-time, building on each other to provide more robust protection than any of these features would on its own. Built on EnGarde Secure Linux and informed by global Threat Intelligence data gathered through Artificial Intelligence (AI), Open-Source Intelligence (OSINT), and Machine Learning (ML), EnGarde is constantly learning from and adapting to the threats that challenge it and updating its protection in real-time to remain ahead of emerging threats and prevent future attacks.  

Stay Threat-Ready with Guardian Digital: A Deep Dive into their Cloud Email Security Services

Let’s take a closer look at the structure of EnGarde, and each feature's critical role in fortifying the inbox against fraudulent and malicious mail.

Open-Source Community Input

Unlike any other solution on the market, EnGarde draws on extensive resources, tools, and intelligence from the vibrant, global open-source community. A product of open-source development, EnGarde is uniquely supported by a collaborative global input program, resulting in rapid updates and superior security and resiliency. In this community-powered development model, emails gathered from millions of systems worldwide are used to identify patterns and perform large-scale tests on filters. The results of these tests are then distributed back to Guardian Digital engineers and incorporated into EnGarde.

Expert Managed vCISO Email Security Services & Accessible Support

Fully-managed vCISO email security services are a vital component of an effective email security solution that is too often overlooked. Ongoing expert system monitoring, maintenance, and support can simplify administration, improve security, and reduce costs, delivering a rapid return on investment (ROI) for businesses. 

EnGarde is managed around the clock by a team of experienced security experts who become a valuable extension of your company’s IT team, partnering with your business in securing its users, critical data, and reputation and acting as the front line of defense against cybercriminals. Our experts work with you to understand your security needs, identify individuals within your organization most likely to be targeted in an attack, and closely monitor them to watch for targeted threats.

Spoofing, Sender Fraud & Impersonation Protection

Email authentication protocols, including SPF, DMARC, and DKIM, help prevent sender fraud and protect sensitive information. These standards verify a sender’s identity and confirm the legitimacy of email communications, safeguarding the inbox against fraudulent and malicious mail.

EnGarde implements SPF, DMARC, and DKIM to the fullest to prevent phishing and spoofing attacks and protect sensitive data in transit. EnGarde goes beyond standard email authentication measures, tracking hundreds of thousands of message attributes, including sender-recipient relationships, domain reputation, email headers and envelope attributes, and message content.

Malicious URL Protection

Phishing is the predominant modern cybersecurity threat that businesses face. Since most phishing emails leverage malicious links to trick users into sharing sensitive credentials or installing malware on their devices, malicious URL protection plays a pivotal role in identifying and blocking these dangerous, costly attacks. 

EnGarde features Guardian Digital URL Protect, offering dynamic malicious URL protection by extracting links from Microsoft Office documents, PDFs, archive files (ZIP, AIZip, JAR), and other file types (uuencoded, HTML) and conducting a dynamic real-time analysis of these files to detect malicious URLs leading to compromise.

Spam & Virus Protection

Spam and viruses are severe, persistent threats to all email users. Spam email is not only annoying, but it can also contain dangerous links and attachments, and an email virus can result in inconvenient and costly downtime for your organization. Traditional spam filters and signature-based antivirus software can no longer protect users, systems, and critical data. Spammers are now using advanced, stealthy techniques such as social engineering to evade spam filters and deceive users, and complex polymorphic viruses can modify themselves to avoid detection. Modern spam and virus protection require advanced, defense-in-depth technologies, such as those seen in EnGarde.

EnGarde features multiple layers of detection engines capable of performing predictive spam and virus detection through heuristics analysis. This advanced technique scans messages for characteristics and behaviors unique to spam emails. The SpamAssassin spam filtration framework is also built into EnGarde’s layered architecture. If SpamAssassin’s software indicates that a message resembles spam, EnGarde quarantines the email, preventing it from reaching the end user. SpamAssassin works with EnGarde’s other detection features to reliably block spam emails while keeping the rate of false positives impressively low.


Once EnGarde’s security features and technologies have scrutinized a message, it is deemed either “malicious” or “safe.” All malicious mail is quarantined, never reaching the intended recipient’s inbox, where it could potentially cause significant harm. Only confirmed legitimate, safe mail is delivered to the end user, mitigating the risk that human error and poor user security practices pose to your organization.

What Are the Benefits of Securing Business Email With EnGarde Cloud Email Security?


Notable benefits of securing your business email with EnGarde Cloud Email Security include:

  • Rapid Return on Investment (ROI): By preventing security breaches, minimizing downtime, increasing productivity, and safeguarding your operations, businesses can expect a positive impact on their bottom line.
  • Better threat protection through an inherently secure design: By applying the collaborative, transparent, open-source development model to email security, businesses receive enhanced threat protection, increased trust in the information they receive, real-time updates, and more secure, resilient technology.
  • Extended IT resources: The ongoing system monitoring, maintenance, and support that Guardian Digital provides reduce the strain on businesses’ overworked IT departments, enabling them to focus on tasks unrelated to email security more productively. These fully-managed vCISO email security services provide the around-the-clock email vigilance required for the early detection and elimination of threats.
  • Better Planning & Policy Enforcement: Complete visibility into your email security and the threats targeting your organization via the EnGarde Cloud Email Security Dashboard reduces risk exposure and enables improved cybersecurity business planning and better enforcement of company policies.
  • Enhanced Microsoft 365 Email Security: EnGarde’s supplementary defenses bolster inadequate built-in cloud email protection to fortify Microsoft 365 email against credential phishing and account takeovers.

Keep Learning About Strengthening Your Email Security Defenses

Is your current email security strategy providing you with the caliber of protection necessary to protect your business against today’s advanced threats? Evaluate your current email security posture using our free Email Risk Assessment Tool

Does your current email strategy have room for improvement? Are you interested in upgrading your email security defenses and protecting your most critical assets with EnGarde? One of our security experts would love to speak with you. Let’s get in touch!

Continue learning about how you can strengthen your email security defenses by exploring the resources below:

  • Implementing a comprehensive email security system can help prevent advanced threats, such as targeted spear phishing and ransomware. 
  • By following these best practices, you can improve your email security posture to protect against cyberattacks and breaches.
  • Keep the integrity of your email safe by securing the cloud with spam filtering and enterprise-grade anti-spam services.
  • Get the latest updates on how to stay safe online.

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