I sit at a computer for most of the day at work, and my work and personal emails are open in my desktop at all times. When I get home, I have my laptop on most always and my email is always open on my desktop. Email is my main form of communication.
Work email should, at minimum, be checked first thing in the morning and toward the end of the day. If not, it would be the same as not answering the phone and not returning messages. Of course, this only applies to workplaces where email has been established as an important method of communication.