TESSIAN

Tim Sadler, Tom Adams, and Ed Bishop were studying at University College London when they realized that most data breaches aren't caused by sophisticated hackers — they're caused by employees making mistakes with email. Sending the wrong attachment.

Clicking a phishing link. Forwarding sensitive data to personal accounts.

In 2013, they founded Tessian to use machine learning to understand email behavior patterns and catch dangerous mistakes in real time.

SaaS subscriptions. Companies pay per-user annual fees for Tessian's email security platform.

The software integrates with Microsoft 365 and Google Workspace. Revenue grows with the number of employees protected.

Proofpoint (owned by Thoma Bravo) acquired Tessian in 2023 to add AI-powered behavioral analysis to its email security suite.

Email Guardian — prevents misdirected emails by detecting unusual recipients. Defender — AI-powered phishing protection that catches spear-phishing and business email compromise.

Enforcer — prevents data exfiltration via email.

Bottom-up adoption. Tessian targeted CISOs at mid-market companies who were frustrated with legacy email security tools that relied on static rules.

The product demonstrated value quickly — catching real misdirected emails in the first weeks of deployment. Customer stories of prevented breaches drove word-of-mouth.

Competing with established email security vendors (Proofpoint, Mimecast, Microsoft Defender). As a standalone email security product, Tessian was vulnerable to being absorbed into broader security platforms — which is exactly what happened when Proofpoint acquired them.

The niche was real but the market was consolidating.

Accel led the Series C. Other investors include Sequoia Capital, March Capital Partners, Balderton Capital, and Citi Ventures.

The acquisition by Proofpoint (a Thoma Bravo portfolio company) provided the exit.