In Mail delivery changes in Exchange 2007, I outlined how Exchange 2007 has been re-engineered in a big way due to 2007’s role-based nature, which necessitated a reworking of how different Exchange services communicate.
The chart below outlines the protocol used to communicate between various roles.
Roles and communications matrix
|From/To||Mailbox||Hub Transport(Same Site)||Hub Transport(Diff.Site)||Client Access||
|Hub Transport(Same Site)||MAPI/RPC||SMTP/TLS||SMTP/SSL||MAPI/RPC||N/A||SMTP/TLS|
|Hub Transport(Diff. Site)||N/A||SMTP/SSL||SMTP/TLS||N/A||N/A||N/A|
Note that there are three primary communication mechanisms:
Where you see N/A, this means that the roles do not talk directly to one another. For example, the Unified Messaging server role talks solely to the Mailbox Server role and never to the Hub Transport server role.
Transition warning: Don’t delete administrative groups
Many organizations are transitioning to Exchange 2007. Bear in mind that Microsoft specifically uses the word transition to describe a process by which an organization moves from Exchange 2000 or Exchange 2003 to Exchange 2007.
Toward the tail end of this transition process, vestiges of the legacy Exchange organization—Exchange 2000/2003 servers, routing groups, etc.—are purged from Active Directory and from the infrastructure. However, exercise some caution before you expunge everything.
In particular, if you’re running legacy Outlook clients (Outlook 2003 and below) don’t remove the administrative groups that once held mailboxes in your legacy Exchange organization. Users’ Active Directory LegacyExchangeDN field continues to point to the legacy administrative group and versions of Outlook before Outlook 2007 use this field in order to find free/busy information.
If you delete these administrative groups, legacy Outlook users may not be able to find or publish free/busy information. Users who have been migrated to Outlook 2007 are not affected by this problem since Outlook 2007 uses Exchange 2007’s new capabilities to provide real-time free/busy information.