Can an employee who insults his superiors in professional SMS exchanges be dismissed?

Mr. [K] was hired as business unit manager by MAPE (the company) on November 4, 2011.

As of September 20, 2016, in addition to his other duties, he was appointed advisor to the Chairman.

He was dismissed on April 17, 2018, for gross misconduct.

The letter of dismissal complains that Mr. [K] of having expressed his refusal to collaborate with the new management to his superior in an email dated January 24, 2018, of having reiterated this refusal to collaborate in mid-March 2018 by refusing to enter his hours in the dedicated software despite two internal memos stipulating such an obligation, and of having made comments likely to harm the company in emails dated December 15, 2017 and February 3, 2018 addressed to company employees, of having openly exposed his differences with the company’s management in front of employees, inciting them to be insubordinate, of having sent SMS messages to four employees in respect of whom the company had initiated dismissal proceedings and of having sent confidential information to one of them, of having advised another to take the matter to the industrial tribunal, of having insulted the company’s CEO in one of these emails and of having denigrated the company. He was also accused of using his personal e-mail address to communicate with the company’s customers.