The Intersite Messaging (IsmServ) service enables message exchanges between computers in an environment with servers that are running the Windows Server operating system. This service is used for mail-based replication between sites. AD DS includes support for replication between sites through SMTP over IP transport. SMTP support is provided by the SMTP service, which is a component of IIS.

The set of transports that are used for communication between sites must be extensible. Therefore, each transport is defined in a separate add-in dynamic link library (DLL) file. These add-in DLL files are loaded into the Intersite Messaging service, which runs on all domain controllers that can perform communication between sites. The Intersite Messaging service directs send-and-receive requests to the appropriate transport add-in DLL files, which then route the messages to the Intersite Messaging service on the destination computer.

If the Intersite Messaging service stops, messages are not exchanged, intersite messaging replication does not work, and site-routing information is not calculated for other services.

This service is installed by default on computers running Windows Server 2008 R2, but it is disabled until the server is promoted to the domain controller role. When the Intersite Messaging service is started in its default configuration, it logs on by using the Local System account.

The Intersite Messaging service is dependent on the following system components:

• DCOM Server Process Launcher
• RPC Endpoint Mapper