Job is demanding

My job is really demanding but that doesn't mean it stops when I get to leave at 6 PM. Before I graduated college and got out in the real world I thought that jobs were something you only had to do 40 or 50 hours per week but then you have free time to decompress and not have to think about work. Boy was I wrong! My boss is constantly e-mailing me on my Westport 4g internet connection at home because he knows I check my e-mail probably more often than I should. I know I dug this hole for myself and I'm the only one who's going to be able to put up some boundaries between myself and the office but it's really hard when you know you're next in line for a big promotion. The last thing I want is for my boss or any of his superiors to think that I'm not dedicated to the job so I feel like for now I have to keep letting them invade my personal time.