It just takes discipline. I'm not a google employee, but I run an online business entirely on my own (and have been doing so for 15 years). I simply don't reply

It just takes discipline. I'm not a google employee, but I run an online business entirely on my own (and have been doing so for 15 years). I simply don't reply to work emails after 6pm, and don't check my email much after that time either. (If I do check my email, it's more to check for personal emails). The only possible urgent thing is if my server goes down. However I get a text message if that happens, so I don't need to keep checking my email. You're not doing yourself any favours by answering emails all night. You will be much more productive if you relax or do something other than work after 5 or 6pm. I also take naps during the day, walk my dog twice a day and/or watch MASH and other TV shows in the afternoon. If you looked in on me you would think I was a lazy bastard, but in fact I'm more productive than any other developer I've ever met.