Often I email staff members and lecturers but don't receive a reply for over a week. This is an issue if it's an urgent email. However if you get an email back saying either they are out of office or backed up with work, then you know where you stand also, if necessary you can ask other people for help instead. But if they don't reply then you are left in the lurch. These emails being compulsory used by staff when necessary would help students and other staff members work ore smoothly and quicker.