I currently have an Exchange 2000 Server in production running Mixed Mode. This is my only Exchange Server and don't have any 5.5 in my environment. There isn't any particular reason why the functional level hadn't been raised, just never got around to it.
Tomorrow I'll be introducing my first Exchange 2003 box to the environment. The question is, do I need to convert my Exchange 2000 box to native mode before I bring in the Exchange 2003 server, or will it be ok if I left it in Mixed mode?