One of Australia's most valuable and promising technology start-ups has been rocked by management upheaval, with the chief executive of Campaign Monitor quitting the company and its Australian co-founders pulling back from day to day roles.

San Francisco-based Alex Bard, who was appointed CEO of the $600 million email marketing company in 2014, has quit to join an undisclosed venture capital firm; while Dave Greiner and Ben Richardson, the company's two Australian-based founders, have relinquished all operational duties, but remain on the board.