I wouldn’t say it’s “normal” across the spectrum of all jobs but for some industries there is an unspoken expectation that you are always contactable. Management Consulting is one of those. I get emails at that time (and later) literally every day.
You can of course choose not to be online/contactable, but that will get you unofficially marked as “career limited”. As in you will never get above average ratings and will be passed over for promotions. Pair that with the fact a lot of consultancies have an “up or out” policy (basically meaning that if you don’t get promoted in the expected time frames you get the elbow) and you can see how you’re effectively coerced into these behaviours. You have two choices… either work for a company like that - you get well paid but have to accept the unwritten “rules”… or just don’t bother and work somewhere with a more structured work pattern.
For the record I didn’t justify his email with a response. I haven’t responded to it since. My response was my notice.
I understand you (and by the way, three cheers to you for not replying), but you see what that implies: in certain companies, for certain jobs, you are assumed to be available 24/7. Well, unless I was a futures trader, or something like that, pulling down a five figure bonus at the end of the year (or six?), and obviously in a job where markets are worldwide and shifting all the time, there is no way I would accept that. No way.
Certain doctors are, I believe, on call like that. That also, you can understand.
Otherwise, I think it's downright rude. Your ex-boss is clearly someone who doesn't have a life. Sad, in a way.
Edit: I should add that I've known a number of people who are actors in my life. My eldest brother, for one (the other one, too, but I have no contact with him). One of my best friends is also an actor. They have to be on immediate call, pretty much. Whoever's hiring can get someone else who's probably as good, in a heartbeat. It's understood.