Continuing a trend that VCs here in London tell me is seeing an increasing amount of deal-flow in Europe attract the interest of top-tier Silicon Valley venture capital firms, TechCrunch has learned that email security provider Tessian is the latest to raise from across the pond.

According to multiple sources, the London-based company has closed a Series B round led by Sequoia Capital. I understand that the deal could be announced within a matter of weeks, and that the round size is in the region of $40 million. Tessian declined to comment.

Founded in 2013 by three engineering graduates from Imperial College — Tim Sadler, Tom Adams and Ed Bishop — Tessian is deploying machine learning to improve email security. Once installed on a company’s email systems, the machine learning tech analyses an enterprise’s email networks to understand normal and abnormal email sending patterns and behaviours.

Tessian then attempts to detect anomalies in outgoing emails and warns users about potential mistakes, such as a wrongly intended recipient, or nefarious employee activity, before an email is sent. More recently, the startup has begun addressing in-bound email, too. This includes preventing phishing attempts or spotting when emails have been spoofed.

Meanwhile, Tessian (formerly called CheckRecipient) raised $13 million in Series A funding just 7 months ago in a round led by London’s Balderton Capital. The company’s other investors include Accel, Amadeus Capital Partners, Crane, LocalGlobe, Winton Ventures, and Walking Ventures.