Email Penetration Testing: Defence Against Phishing Attacks

Why email is still the #1 cyber threat

Email continues to be the main attack vector for cybercriminals, a fact driven not only by it being the most widely used communication tool in business, but also by the evolving sophistication of cyber threats. Despite advancements in cybersecurity, attackers continue to exploit human vulnerabilities to bypass technical defences. A well-crafted phishing email can trick unsuspecting employees into revealing sensitive information, downloading malware, or authorising fraudulent transactions, making email security a critical concern for organisations of all sizes.

And the following numbers back it up:

• 91% of cyberattacks start with a phishing email [1]
• 68% of breaches involve human error (often from social engineering) [2]
• Email scams cost businesses billions every year, with Business Email Compromise (BEC) alone causing over $50 billion in reported losses [3]

Security awareness training is important - but is it enough to prevent phishing attacks? If you’re not testing your email security with social engineering and real-world attack simulations, you’re leaving your business vulnerable. Simulating actual attacks can help your business identify not only technical misconfigurations but also test employee responses, providing a thorough view of your organisation's security posture.

This is where email penetration testing comes in.

What is email penetration (pen) testing?

Email pen testing is an advanced part of our social engineering services, designed to simulate real-world phishing and spoofing attacks against your organisation. Unlike standard phishing simulations that only measure if employees click on suspicious links, full email penetration testing delves deeper. It rigorously tests the entire email security framework—from the human element to the technical defences—to expose vulnerabilities before actual attackers can exploit them.

At its core, email penetration testing involves a controlled, ethical attack that mimics the tactics used by cybercriminals. And the goal? To identify weaknesses in your organisation’s defences so you can proactively address them. This method provides valuable insights into both the susceptibility of employees and the robustness of your technical security measures.

The process evaluates several critical areas:

• Phishing susceptibility – are your employees falling for sophisticated, well-crafted phishing emails? Testing can reveal how likely they are to click on malicious links or divulge sensitive information.
• Email spoofing vulnerabilities – can attackers impersonate trusted figures like your CEO or the finance team? Simulating spoofing attacks can assess whether your organisation’s communication channels can be easily manipulated.
• Weaknesses in email authentication (DMARC, SPF, DKIM) – is your domain properly secured against misuse? The testing process examines your email authentication protocols to ensure that configurations like DMARC, SPF and DKIM are optimally set up to prevent unauthorised use.

With email pen testing, you don’t just educate your employees - your technical defences are hardened and the gaps in your security stack are exposed. By understanding exactly where your vulnerabilities lie, you can implement targeted measures to reinforce your email security, reduce risk, and build a more resilient organisation.

Why traditional security measures aren’t enough

Most businesses already have some level of email security measures in place - so why is phishing still so effective?

• Spam filters aren’t fool proof – although spam filters block many unwanted messages, advanced phishing attacks use convincing domains, clever wording, and even familiar sender names to bypass email security gateways. Cybercriminal tactics are continuously adapting, making static filtering less effective over time.
• Multi-Factor Authentication (MFA) isn’t a silver bullet – MFA adds an extra layer of security, but it’s still not invulnerable. Attackers work around it by exploiting session hijacking and adversary-in-the-middle (AiTM) techniques, intercepting or stealing login tokens despite the extra verification step.
• Email authentication (SPF, DKIM, DMARC) is often misconfigured – proper email configuration is critical to prevent spoofing - if these aren’t set up correctly, it can allow attackers to masquerade as trusted senders, spoof your domain, creating an easy pathway for phishing and fraudulent activities.
• Security training isn’t enough – regular security training is essential but even well-trained employees can fall victim to highly convincing phishing scams, especially when under pressure, or when the attack appears unusually urgent or familiar. The human element remains the weakest link, and attackers exploit our natural tendency to trust.

The best way to truly measure and mitigate your risk is to simulate real-world attacks with email pen testing – this proactive approach exposes exactly where your defences break down, allowing you to address security gaps before cybercriminals have a chance to exploit them.

How email penetration testing works with Bulletproof

At Bulletproof, our team of CREST-accredited ethical hackers are dedicated to staying one step ahead to uncover vulnerabilities before cybercriminals can exploit them by performing in-depth email security testing. Our approach is methodical, realistic, and tailored to your organisation’s unique threat landscape.

1. Scoping & planning – we work with your team to define clear objectives and outline the test parameters. This planning stage ensures that our simulations accurately mimic the real-world threat scenarios your organisation may face, from phishing attempts to more targeted, sophisticated attacks.
2. Reconnaissance – leveraging Open Source Intelligence (OSINT), we gather publicly available data to understand your organisation’s digital footprint, allowing us to craft highly realistic phishing and spoofing attempts that reflect the tactics of actual cyber adversaries.
3. Attack execution – we simulate a range of targeted attacks, including phishing, email spoofing, and social engineering techniques to assess not only employee's awareness, but how they respond to suspicious emails, and the effectiveness of your technical safeguards. This step is critical in revealing both human and technical vulnerabilities.
4. Security assessment – we analyse your email authentication settings (SPF, DKIM, DMARC) to identify misconfigurations that could allow attackers to spoof your domain, ensuring that all technical defences are properly aligned to prevent unauthorised access.
5. Detailed reporting & actionable fixes – after completing the tests, we compile a comprehensive report that highlights every identified vulnerability along with clear, actionable recommendations. This report serves as a roadmap to help reinforce your email defences and mitigate risks effectively.

By proactively running these real-world tests against your email security, Bulletproof empowers your organisation to identify and address potential breaches before they occur, ensuring that your defences are robust and resilient against even the most advanced threats.

Key takeaways: why you need email penetration testing

• Identify weaknesses before attackers do – simulated attacks expose vulnerabilities in your email security setup. By pinpointing these gaps early, you can address them proactively, reducing the risk of a real-world breach.
• Test employee awareness in a safe environment – assess how your team responds to sophisticated phishing attempts without real-world consequences. This controlled testing identifies which employees are vulnerable and highlights areas where further training is needed.
• Strengthen email authentication – ensure that your SPF, DKIM, and DMARC are properly configured. Proper authentication is key to preventing attackers from spoofing your domain and compromising your organisation’s credibility and security.
• Reduce your risk of Business Email Compromise (BEC) – simulating attacks that mimic BEC scenarios can help us better understand your exposure to fraudulent transactions and data breaches. This insight is crucial for implementing targeted defences against financial fraud and unauthorised access.
• Enhance security policies & training – the actionable insights gained from penetration testing enable you to refine your security policies and improve company-wide cybersecurity awareness. Continuous improvement in training and protocols helps build a more resilient defence against evolving cyber threats.