Deployed inside your Active Directory directory service forest, the Hub Transport server role handles all mail flow inside the organization, applies transport rules, applies journaling policies, and delivers messages to a recipient's mailbox. Messages that are sent to the Internet are relayed by the Hub Transport server to the Edge Transport server role that is deployed in the perimeter network. Messages that are received from the Internet are processed by the Edge Transport server before they are relayed to the Hub Transport server. If you do not have an Edge Transport server, you can configure the Hub Transport server to relay Internet messages directly. You can also install and configure the Edge Transport server agents on the Hub Transport server to provide anti-spam and anti-virus protection inside the organization.
The Hub Transport server role stores all its configuration information in Active Directory. This information includes transport rules settings, journal rule settings, and connector configurations. Because this information is stored in Active Directory, you can configure settings one time, and then those settings are applied by every Hub Transport server in the organization.
The message-processing scenarios that you can manage on the Hub Transport server role are described in the following sections.
Internal Mail Flow
The Hub Transport server role processes all messages that are sent inside the Exchange 2007/2010 organization before the messages are delivered to a recipient's Inbox or are routed to users outside the organization. There are no exceptions to this behavior; messages are always passed through a server that runs the Hub Transport server role.
Messaging Policy and Compliance Features
A collection of transport agents lets you configure rules and settings that are applied as messages enter and leave the mail flow components. You can create messaging policy and rule settings that are designed to meet different regulations and that can easily be changed to adapt to your organization's requirements. The transport-based messaging policy and compliance features include server-based rules that you configure to enforce your organization's compliance scenarios and the Journaling agent that acts to enforce message retention.
Anti-Spam and Antivirus Protection
The Exchange 2007/2010 Built-in Protection features provide anti-spam and antivirus protection for messages. Although these Built-in Protection features are designed for use in the perimeter network on the Edge Transport server role, the Edge Transport agents can also be configured on the Hub Transport server. By default, these agents are not enabled on the Hub Transport server role. To use the anti-spam features on the Hub Transport server, you must register the agents in a configuration file and enable the features that you want to use by running a provided Exchange Management Shell script. You install and enable the antivirus agent in a separate operation.
The error-free functioning of the Hub Transport server is therefore essential to ensure uninterrupted mail flow within the Exchange organization and to insulate the Exchange organization from spam/virus attacks. By continuously monitoring the operations of the Hub Transport server, administrators can be promptly alerted to ineffectiveness of the anti-spam or anti-virus agents on the server and slowdowns in the processing of mail messages by the server. This can be achieved using eG Enterprise. eG Enterprise offers a specialized monitoring model for continuously monitoring the Hub Transport server to track mail flow and timely provide alert on slowdowns.