If there's something I need to do I either write a note down on a scrap-of-paper/notepad/sticky-note or just you know, do it.
I am in fact hilariously unorganized but it's pretty unimportant because I'm not sure how having a bunch of folders for stuff is supposed to keep me from forgetting to do things.
talking to the developers, thats not exactly how they intended the software to be used, and internally they close tickets aggressively and move longer term tasks to project management tracking in trello.
on the gmail front, their tabs or whatever are a lifesaver. i only check the primary and update tabs daily, the rest is pseudo-junkmail.
tldr: to answer your question simply. if i get an email asking for something or that i need to act on, and it didnt come FROM some type of tracking/pm/ticketing software, i forward it to the appropriate software so it is added to the todo list. if youre on a team using task software like https://glip.com/ for instance, you add the task directly in the software, you dont email the person.
human<>human communication is almost always through messaging apps.
producthunt had this today https://www.producthunt.com/tech/owlie
no matter what, i rely on search. if i need to find something in facebook messenger, i use search. gmail, search. outlook, search.
if an email is important, i star it. if i need to plan with mother and sister, i send a message to a family IM group.
virtually every message i send is 1) through a routing abstraction layer on one of the two ends 2) instant messaging 3) social forum. direct email to email chitchat isnt a regular practice, but that doesnt mean i dont use email. email for me functions as a 1)compatibility layer between otherwise isolated systems 2) old school notification tray
So you don't actually use email as a communication system, in case you misunderstood my meaning. I'd be interested to see whether this is generally true for people who argue that they don't need to worry about what's in their inbox.
if i did hold conversations directly through email<>email, that would not change my lack of folders. i could see using gmail tags more aggressively.
the closest thing i have to folders are saved, predefined search queries based on parameters and conditions. the contents of those sort automatically based on metadata, some of which i apply by hand.