Clearswift was founded as NET-TEL in 1982. One of the co-founders, John Horton, had previously worked at
GEC and
Acorn Computers. In 1988, NET-TEL launched
Route400, the world's first mail client for
MS-DOS (using the
X.400 protocol). It was later ported to other platforms. In 1998, NET-TEL switched its main business to content filtering, as the popularity of the
Microsoft Exchange Client took away the mail client market. In 2002, Clearswift acquired Content Technologies from
Baltimore Technologies, along with the MIMEsweeper brand. Clearswift extended the MIMEsweeper line to include web and instant messaging filtering. These were marketed as protecting against the leakage of confidential company information on social networking sites - Clearswift argues that instead of banning Web 2.0 sites and services entirely, businesses can actually gain a competitive advantage by making use of them, provided their use is monitored. In 2003, the company received $6.07 million from its shareholders, including venture capital funds managed by
Amadeus Capital Partners, BA Capital Partners, Cazenove Private Equity, and
Kennet Partners. Also, it was reported that Clearswift were the providers of a new email filtering system at the
House of Commons, responsible for blocking Welsh language emails as "inappropriate content", and preventing MPs receiving copies of a Sexual Offences Bill. Clearswift would not confirm that the House of Commons was a customer, citing customer confidentiality reasons. In January 2008, failure to renew a domain name caused loss of email services to 5% of Clearswift's customers. In Dec 2009, Clearswift sold the
Deep-Secure, Bastion and Flashpoint products in to a spin-off company, "Deep Secure". In November 2011, Clearswift was sold to Lyceum Capital. In August 2012, Clearswift acquired Jedda Systems Pty Ltd. In February 2013, Clearswift acquired Microdasys in order to strengthen its web product line. In January 2017, Clearswift was acquired by Swiss defense company
RUAG as part of its RUAG Defence Cyber division. In December 2019, Clearswift was acquired by HelpSystems to expand its cybersecurity portfolio. ==Research & development==