Email is everywhere.
Disks are cheap.
I'm drowning in email (and I don't mean the spam, which gets deleted on sight - if it even reaches my heavily filtered mailbox).
An old plan, has been to create an email repository based on Metakit. With all sorts of nifty associative and non-linear access mechanisms, because that's how the mind works, and that's how old emails can probably best be found again.
It hasn't happened so far.