Your email box is not a filing cabinet. Allison says "Uh, YEAH it is!"
I have to disagree with this article. If you have a nicely streamlined email service (gmail, for example), I think it’s perfectly alright to use it as storage. I still clean it out pretty regularly (newsletters, expired offers, etc). But it’s so easy and efficient to just run a search with a name or a word that will lead you to directly where you need to be.
Plus, a lot of the time, I don’t realize I DO need to refer back to an old email until months after the fact, and then I’m happy I didn’t get rid of it in a fit of cleaning.