Rule #2: Immediately move obligations out of your inbox and into role-specific repositories.
I currently inhabit four professional roles: writer, teacher, researcher, and director of graduate studies for my department. For each of these roles, I set up a Trello board that includes a column for: things I’m working on actively, thing I’m waiting to hear back about from someone else, things on my “back burner” that I’m not yet ready to tackle, and a list of ambiguous or complicated things that I need to spend some time on figuring out. Every email I receive immediately gets moved to one of these columns in one of my Trello boards.
I actually have a client right now that is mostly a pain to work with because they won't respect the above. I have a role specific repository for client project management (Github) and they simply email me all the time.
That means their comments are caught up with other email, like all the stuff coming from my children's teachers, and I miss it. Or I have to hunt for it.
It's unlikely I'll work with the client after this brief few hours because of their lack of use of project management. After over a decade of running software projects, one of the big ways to ensure a project will fail is not sticking to project management.