The One Security Mistake That Could Kill Your Startup (It’s Not What You Think)

Jan de Vries · 2026-07-16

Ask a founder what keeps them up at night, and you’ll hear about runway, hiring, and product-market fit. Rarely the inbox. Yet the data is stubborn on this point: according to IBM’s Cost of a Data Breach Report 2025, phishing was once again the most common initial attack vector, responsible for 16% of breaches analyzed, at an average cost of $4.8 million per incident. A Verizon Data Breach Investigations Report (DBIR) adds that a human element—phishing, stolen credentials, or social engineering—is involved in roughly 60% of all breaches. For early-stage companies, the math is even less forgiving. A corporate giant can absorb a seven-figure incident; for a Seed-stage startup, a compromised inbox that leaks customer data or reroutes an investor wire transfer can be existential. And the attackers know it: business email compromise (BEC) alone caused $2.77 billion in reported losses in the US in 2024 across 21,442 complaints, according to the FBI’s Internet Crime Report. Europe’s cybersecurity ecosystem is responding, evidenced by a wave of startups building defenses against these threats—from deception technology that tricks attackers into surrendering stolen credentials to a broader cohort of European cybersecurity startups. But most breaches don’t happen because a company lacked cutting-edge tooling. They happen because founders got the basics wrong. Here are the five mistakes that come up again and again. ### Mistake 1: Treating Email Security as an IT Problem for Later In a five-person startup, “IT” is whoever set up the workspace account in week one—usually with default settings and usually in a hurry. The problem is that email isn’t just a communication channel; it’s the master key to everything else. Password resets for your CRM, your cloud console, and your banking portal all flow through the inbox. Once an attacker controls a founder’s email, they effectively control the company. The fix costs almost nothing: enforce two-factor authentication (ideally hardware keys or passkeys rather than SMS), require a password manager from day one, and choose a business email provider where security is the default rather than an add-on. Privacy-focused services built in Europe come with end-to-end encryption, phishing protection, and GDPR-aligned data handling out of the box—which matters when your “security team” is one overworked CTO. Whatever provider you choose, the point is the same: the decision you make in week one is the one you’ll be living with when you’re 50 people. ### Mistake 2: Assuming Your Team Can Spot a Phish Awareness training built for the 2015 threat landscape—with its misspelled sender names and clumsy grammar—is now dangerously outdated. IBM’s research found that generative AI has cut the time needed to produce a convincing phishing email from roughly 16 hours to about 5 minutes. The telltale signs founders tell their teams to look for are disappearing. Startups are especially exposed because of who they hire and how fast. Research from security training firm Keepnet found that new hires are 44% more likely to fall for phishing than longer-tenured staff, and 71% click a phishing email within their first 90 days. If you’re doubling headcount every year, a large share of your company is permanently in that high-risk window. Training still matters, but it has to be continuous and simulation-based—not a one-off onboarding slide. ### Mistake 3: Ignoring the Money-Movement Problem BEC attacks don’t need malware. They need a plausible email—supposedly from the CEO who is traveling and urgently requesting a transfer—and an employee who wants to be helpful. The Verizon report puts the median loss from a single BEC incident at around $50,000, which for many early-stage companies is a month or more of runway. Fundraising periods are peak season: wire instructions get sent, urgency is high, and attackers exploit that chaos. The fix isn’t complicated: implement a two-person approval process for any transfer over $5,000, verify payment requests out of band (a quick call or in-person confirmation), and never trust a single email as authorization. > “The moment you start scaling, your inbox becomes the most dangerous tool in your company.” ### Mistake 4: Overlooking Third-Party Email Risks When you’re a startup, you rely on dozens of third-party tools—Slack, Notion, Stripe, and a hundred others. Each one is tied to an email address, and each one is a potential entry point. A single compromised third-party account can cascade into a full breach if that account has access to your email or sensitive data. Conduct a quick audit: list every service that has access to your company email. Revoke unused permissions, enforce single sign-on where possible, and monitor for unusual login attempts. It’s a 30-minute task that can save you months of damage control. ### Mistake 5: Not Having a Breach Response Plan Most startups don’t think about what happens after a breach. They assume it won’t happen to them. But when it does—and the data says it will—the first 24 hours are critical. You need a clear plan: who shuts down access, who notifies customers, who contacts law enforcement. Draft a simple one-page response plan today. Include contact numbers for your email provider, legal counsel, and a cybersecurity incident response firm. Test it with a tabletop exercise. It’s not about paranoia; it’s about being prepared for the reality that every startup faces. The bottom line? Email security isn’t a future problem. It’s the foundation of your company’s survival. Get these basics right, and you’ll sleep better at night—even if the inbox never stops buzzing.