I use the word "inbox" in the generic GTD sense, i.e. anywhere that "stuff" can accumulate, awaiting processing. At work, I receive a lot of emails. I also go to a lot of meetings at which I pick up ...
After following GTD principles for several years, I now have the system well oiled. Unfortunately, I'm still overloaded--not at the inbox level, but at the project level. Too many things are flowing ...