Does Exchange Server 2003 add any new features when running in Exchange native mode?

Exchange 2003 doesn't provide a new native mode—all Exchange organizations are either mixed mode (i.e., a mix of Exchange 2003, Exchange 2000 Server, and Exchange Server 5.5 servers) or native mode (i.e., no Exchange 5.5 servers). Don't confuse these Exchange modes with the Windows native and mixed modes; they're quite different.

A native-mode Exchange organization that contains only Exchange 2003 servers provides three interesting new features:

  • Full support for query-based distribution groups—To create a typical distribution group, you must manually add and remove members. To create a query-based distribution group, you write a Lightweight Directory Access Protocol (LDAP) filter rule (like the ones you use to create address lists) that specifies who the group's members should be. You can use these groups in an Exchange 2003/Exchange 2000 mixed environment, provided you use the Exchange 2003 setup program to apply the Exchange 2003 schema changes.
  • Full use of 8-bit MIME between routing bridgehead servers—The Internet standard for moving binary content has long been used to convert 8-bit characters to a 7-bit encoded representation. This conversion requires about 30 percent more network space than the native 8-bit encoding. Exchange supports the 8BITMIME SMTP verb, which tells the receiver that the data being sent isn't encoded. As a result, using 8BITMIME in a native-mode Exchange organization between routing bridgehead servers results in significant bandwidth savings.
  • Automatic removal of zombie access control entries (ACEs)—When you migrate from Exchange 5.5 to Exchange 2000 or Exchange 2003, you can end up with several ACEs that contain the SIDs of objects that didn't get migrated. These ACEs are particularly troublesome for public folders because the folder ACLs apply to all users. Exchange 2003 can automatically strip ACEs that contain SIDs for objects that don't exist in the directory, but this feature works only after you've removed the Exchange 5.5 servers.