The last [US] BigCorp I worked for deployed (in Outlook) automatic deletion of all emails older than their Records Retention threshold. It was incredibly frustrating to have essentially all design/rationale history (from the key players involved) go into the auto-shredder with nobody but me caring. The only workarounds that could avoid the auto-shredder were enormously labor intensive, and of course, debatably violated Record Retention policy.

I never understood the mindset which seemed to interpret “we must preserve this for 5 years” as “we must _delete_ everything after 5 years”. I understand they want to minimize storage costs but they are destroying institutional knowledge. I have recently wanted to refer back to my notes on some older services and discovered that all my old notes have been deleted.

I think the rationale is that they don't want any liable behavior to be discoverable. Institutional knowledge could be in a controlled document storage and the email thread where you negotiated some kickbacks 6 years ago is shredded.