This is so that the employer do not "politely suggest" that you should check your email just in case, or that if you don't comply they will take measures. You

This is so that the employer do not "politely suggest" that you should check your email just in case, or that if you don't comply they will take measures. You know it's not mandatory to check your email but if you don't do it you will be fired for another spurious reason.