The surveys checked how long people usually spent replying to emails off the clock, as well as their reported ability to mentally detach from their job duties after office hours.
The scientists found that employees who reported working for organizations with high expectations to monitor email after-hours were less able to detach from work issues at home, and felt more emotionally drained according to the study co-author Liuba Belkin, Ph. D.
Moreover, such people spent 8 hours per week replying emails after work which is an equivalent of an extra full day at the office.
More details here.