Along with that, there’s philosophy of ‘never look at an email twice.’ The idea being: read an email and take care of whatever needs to be done. If you’re not ready to take care of it, don’t check/read email.
Ideally, you keep your inbox empty: Inbox Zero
I tend to keep 3-4 emails in my inbox that are basically the equivalent of ongoing files. I could save them as files, but that would actually make my system more complicated.
Followupthen is a great way to get and email out of your inbox (and mind) when you can’t/don’t need to take care of it then, but don’t need to look at it until it’s time.
If someone asks me to ping them on Thursday, I just forward that email to ‘firstname.lastname@example.org’ and delete it.