I completely disagree. I've kept every email I've ever received or sent since 1996 (close to a million emails, all searchable/indexed) and it has proved extreme

I completely disagree. I've kept every email I've ever received or sent since 1996 (close to a million emails, all searchable/indexed) and it has proved extremely useful over the years to be able to find ancient emails very quickly. I'm sure some large proportion of those emails I will never use, or will never be useful, but space is cheap, and keeping them doesn't hurt at all.