Research by Dr. Thomas Jackson http://homepage.ntlworld.com/cotwj1/top5downloads.html
The Atos Group, in The Guardian: We spend 40% of our workday on internal mail:
http://www.theguardian.com/housing-network/2012/dec/17/ban-staff-email-halton-housing-trust
Researcher Gloria Mark on email-induced stress, in FastCompany:
Lee Mallon from Rarelly Impossible, interviewed by the BBC:
http://www.bbc.com/capital/story/20150324-the-companies-that-banned-email
Business Insider talks about French company Atos, who came off email: