Employee leaves the company, what to do with email account, forward or alias to someone else?

Pretty noob question..but do I use an Alais or Forward to send onward any new emails sent to a Ex-employees account.

EDITED for Clairity:

It's already a policy from management when an employee leaves, to make sure that any new emails that our ex-employee receives, are sent onward to the manager of the department. I'm curious of the best way to do that because there is 2 ways.

• 1) On the account of the now Ex-employee, put a forward on it, the account sits as is, but any mail is forwarded to so-and-so.

• 2) On the account of the Manager, I place an alias that is the Ex-employees address. Like: salesguy1@a.com is Fired... so the email account managerofsales@a.com now has an alias of salesguy1@a.com