To redirect exchange email from one account to another:

1. Open active directory users and computers
2. Find the account you want to redirect mail from
3. Open the properties box for the account by double clicking on it
4. Go to the “Exchange General” tab
5. Click “Delivery Options”
6. Select the “Forward to” radio button
7. Click “Modify” and choose an account or a contact from the active directory
8. Optionally check “Deliver messages to both forwarding address and mailbox” if you want this account to continue to receive email.
9. Click “OK”  and “OK” or “Apply” to save the changes

Note that to forward to an external email address you must first create a contact in active directory.

To redirect email and remove the account or permanently redirect email you could remove the email address from the source account and add it to the destination account or perhaps better create a distribution group with this address and add the target user to the group.