I work in an office where email is the dominant mode of communication. Whereas bureacracies of the past jumped to the beat of Memos, and moved files from desk to desk, email is the medium for all such communication now. Email is used for all sorts of things, from simple requests, to transferring large work documents.
The amount of email that each of us has to process (and I do mean process - on some days, your work is clearing email) can hit highs of hundreds: I once came back from a week's leave to find 300 emails staring me in the face. I spoke to a colleague last week who told me that going on leave incurs great anxiety for her, because of the anticipated log-jam of emails she'll need to clear after. The first time I had to do this, it took me 2.5 days to clear everything.
Coping mechanisms have to be adopted. Most of us prefer to work on a face to face basis: after 3 years here, we'd much rather take a walk to the other workstation and talk things over in person (helps to combat "cubicle butt" as well - the result, I'm sure, of blood pooling in your bottom after a few hours of sitting down). I've also learned that clearing email, especially the backlogs after a stretch away, is a "bottom-up" process: start from the bottom, read the fwd:fwd:fwd: emails, and eventually you'll reach a point where all the emails are redundant and no longer relevant.
Delete ruthlessly beyond that point. If it hasn't been solved in all the time you were away, someone will bring it to your attention again. Delete ruthlessly all spam, or spam-like emails - the "Hey everybody I found this hilarious video/photo/joke" emails.
All this triggered off by reading this man's analysis of his email usage over the past 8 years: Eight Years of Email Stats. (note the increase in the amount of spam in the last 3 years)