adding a new exchange 2003 mail name

My company has an existing email address (example red.org). we are changing our name to (example blue.org). our current email cannot be removed since lots of people have it. how can I add the new mail name to my company and use both temporarily to then delete the old one in a few months. do i need to create new domain or new forests or with just new suffixes will this work and how to do this. Thanks in advance.