Ex-empolyee Email?

How do you handle business continuity when someone leaves? I am finding mailboxes active for people who have not been with the company for more than 6 months.

Do you transfer emails to the new person?
Allow the new person access to the old account?
Change the name from oldperson to newperson?

We are a US company. I have a feeling we are crossing some legal boundaries I would rather not.