I’m not sure if it’s the “best practice,” but we simply add a new SMTP address for the user, set it to the primary email address, and keep the old one for awhile. We also change every instance that we can for Active Directory/Exchange fields. The only one that I believe that cannot be changed is the x.400 address, but that doesn’t really matter to us. x.400 is used internally on Exchange only.
You probably also want to change the user profile and home directory if you associate it with their full username or lastname in any way. You can simply change their roaming profile folder/directory and profile location as well as the home folder. The permissions should be the same because it’s the same SID for the user.
Hope that helps,