The reason I don't is because it tacitly sets an expectation for the recipient(s) that they do the same.

I agree, though sometimes you are working at a particular time and need to get things out of your queue. The onus is on each person to switch off non-emergency notifications out of hours and preserve their personal time.

I also think it's crucial to never reply quickly to non-emergencies. Just creates the expectation you're available and encourage more of the same.

That is, unless it's a situation/relationship you want to foster to establish yourself in a team, outpace someone for promotion, etc.

I'm not saying you shouldn't work when you want to / have to. Just do your best not to broadcast that you are, because that's how expectations get set unrealistically across a company.

I sometimes send emails out of hours but I have absolutely no expectation that they will be replied to soon and I do not check or reply to emails after hours. Sometimes I just have something I need to send before I forget or remember that I forgot to reply to something.

Sure, but the more people do this the more managers expect it.