If I ever have employees that check their work email at weeknights or weekends it will lead to a disciplinary!
There are few more destructive habits for your peace of mind, home-life and hobbies, and ability to maintain relationships. If your boss has an emergency they can call you, and getting a head-start on Monday morning is messing your head up for the other things your life should consist of.
How can you expect to devote attention to family and friends, to a successful hobby or aspirations outside of work if you are keeping your mind in your workplace problems all the time?
Never allowing your mind to change gears and context-switch away from work could also mean you feel less rested by Monday morning, and less able to see the problem from another angle.
Do yourself, and your boss, a favour and spend your outside hours on non-work stuff. Unpaid additional mental stress working outside hours is a nonsense, and you are unlikely to be rewarded for it with anything other than even more work to fill up your personal time.