Europe (Netherlands) here, where I've worked so far, you would not expect a mail to be read and answered out of (individual) work hours. Only if things went south and someone was needed (because the company was too small to make all expertise fully redundant and sync up holidays), after a lot of hesitation, help would be asked (!).

Now I'm running a startup with 1 cofounder, we Slack also in evenings and weekend, but there's no real expectations there either. We just both prefer to be flexible (wrt work-life and life-work) and put in a bit of effort right where it is needed instead of hammering all the time.