iOS does that, maybe, but Android doesn’t. The mail client I use on my Android phone notifies me in a timely fashion when new mail arrives, often in less than a second. It just uses IMAP’s IDLE command to wait for new mail. If the connection drops it can just open a new one.
Does it occur to you that there are so many different variants of Android and they all do their own thing regarding background processes? It is so complicated that you can find websites like this https://dontkillmyapp.com/
That’s a fair point; I hadn’t realized how bad certain brands could be. The last Samsung phone I owned was from about 10 years ago, and it worked just fine. I replaced it with a Google Pixel last year when the 3G networks started getting shut down, and it works great too.