Deleting email can sometimes be construed as destruction of evidence.
From what I know, the way this is addressed is through policy. For example, company sets policy of retaining 3 months of email. Company follows this policy. Then, email that is deleted that is more than 3 months old, is not considered destruction of evidence.
Anyway, there's too much stuff that isn't spam but has only momentary utility to keep everything. For example, automated notices are usually very high volume and always no longer useful within 12 hours.
From what I know, the way this is addressed is through policy. For example, company sets policy of retaining 3 months of email. Company follows this policy. Then, email that is deleted that is more than 3 months old, is not considered destruction of evidence.
Anyway, there's too much stuff that isn't spam but has only momentary utility to keep everything. For example, automated notices are usually very high volume and always no longer useful within 12 hours.