There is a Discourse on what we might call email discipline. Here are a few related takes.
There are those who simply don’t respond to email at all. These people are demons and you should pay them no mind.
Relatedly, there are those who “perform” some kind of message about their non-email responding. Maybe they have a long FAQ on their personal website about how exactly they do or do not want to be emailed. I am not sure I actually believe these people get qualitatively more email than I do. Maybe they get twice as much as me, but I don’t think anybody’s reading that FAQ buddy. Be serious.
There are those who believe it is a violation to email people off-hours, or on weekends or holidays, or whatever. I don’t agree: it’s an asynchronous communication mechanism, so that’s sort of the whole point. I can have personal rules about when I read email and these depend in no way on my rules (or lack thereof) about when you send them. Expecting people to know and abide by your Email Reading Rules FAQ is just as silly.
I have an executive function deficit, diagnosed as a child (you know the one), and if you’re lucky, they teach you strategies to cope. I think non-impaired people should just model one of the best: email can’t be allowed to linger. If it’s unimportant, you need to archive it. If it’s important you need to respond to it. You should not have a mass of unopened, unarchived emails at any point in your life. It’s really that easy.