Unfortunately, those goals are rarely communicated and accepted by the people they're imposed on.

My first full-time job had an unexplained email expiry policy. After being frustrated several times at losing some explanation on how/why, I started forwarding all my emails to gmail. In retrospect, that's probably a worse result to whoever imposed the expiration.

Fortunately, these days people are better about consolidating knowledge on wikis or some kind of shared docs instead of only email.