I have seen it before and, like last time, I really think I should follow some of this... I'm very bad at single-tasking and it doesn't help at all getting things done.
My inbox is a monster. Usually I've something like 4000 emails in my gmail inbox, I read most of the things, reply almost only to very important emails if I'm busy. All the rest is a flow - like twitter.
Email is not a serious thing this days. It is too simple to send one, and people keep writing emails about things not important, or that are trivial to figure without any help, containing a lot more words than needed to express an otherwise simple message and so on.
Do you really want to pass half of your life reading/writing emails about things that don't interest you? I don't want. This is one of the things that may affect your work performance in a critical way.
My gmail inbox used to be like that until a friend of mine, visiting me, got so annoyed with it he archived the lot (with my permission).
Trying to stick at inbox zero after that has been a definite improvement, but it does make for painful periods when I'm away for a day and come back to a ton of unread rubbish I'd normally just archive as soon as it came in. Theoretically select-all-unread-archive is easier than interrupting focus, archive, resuming focus, but the mental burden of 200+ unread messages is not to be underestimated.
http://practicalist.com/singletasking.pdf