So instead draconian lawyers and corporations do the following:
1) Delete email older X months old => Wasting time and money when employees have to replicate work because they can't find information in their email.
2) Hide criminal behavior by destroying evidence.
An organization with integrity wouldn't delete email to save themselves from a lawsuit. They'd delete email because the storage costs exceeded the likely future value. Which with the cost of storage being so low that is basically never. I can vaguely see forcing users to download their old mail locally [ie. Outlook's AutoArchive feature], thus removing that storage from the server which has higher IT labor then my desktop. But I don't think corporations should force users to not archive mail either by IT rules or by domain policy settings [at my work Outlook can't download mail to a local PST because they've disabled that feature, yet anything stored on the server is deleted after 1 year]
Email should be held indefinitely while a user's account is active simple as that. Any deletions, subject to legally required retention rules, should be done at the users discretion. 1 year retention after a user is fired/quits seems reasonable for non-active users. Otherwise your discovery just get's harder as users download their email for future reference to who knows where... Make memo's on random network drives, post it notes in their office, you get the idea.
If discovery happens corporations should stand by their actions. If they were illegal or unethical, they should face the music at the lawsuit/criminal proceedings. Simple as that. But there is a simple solution to that problem too: Don't do sketchy things..