One user with multiple aliases in Exchange

How would I set up a user with two different names in Exchange? Say I have a user that needs 2 email addresses:

james@company.com
parts@company.com

The account is set up under James and I added an smtp entry for parts@company.com and both of those work fine externally. But when someone internally types parts into their outlook mail to send a message it bouces back. I tried adding a parts@company.local but that did not work.

Any ideas?

Thanx.