Been thinking during this week of lower flow email that email overload is a real thing, and it is solvable, but that the approach is not "a better mail client". The answer is a better way to do the stuff you do inside email.
What you do inside email varies -- calendaring, task management (as PG says), catching up with friends, discussions about work stuff, funny forwards... what else?
What's inside your email?
Some background = http://a.sarva.co/2012/12/reading-paul-graham-on-the-re-invention-of-email/
In other words, help me figure out what my next startup should be about (me = cofounder Virgin Mobile USA, IPO and Peek, acquired).
I open a new draft email and set the subject as "Board meeting 30th December 2012". Then I jot down quick notes when I need to in bullet points.
I do the same when I'm interviewing someone (after letting them know that I'm listening but that it's important that I take notes about some of the technical areas we ask about). When I look inside my drafts folder I see a nice list of events that I took notes at.
It also works great when you wake up in the night with a new idea or blog post which you want to jot down. I can head save the draft, then pick it up on my phone on the way in to work.