Anti-spam filtering in Exchange is performed by anti-spam agents, which are a type of Exchange Transport Agent. Transport Agents perform processing on incoming or outgoing messages at particular points in the message pipeline (most points are during an SMTP session with another mail server).
Exchange Server includes several built-in transport agents, such as the Transport Rule Agent. There are also built-in anti-spam agents which are not installed by default. All of these built-in agents are shown in the System Transport Agents section in QSS Exchange Anti-Spam Toolkit.
QSS Exchange Anti-Spam Toolkit provides two additional transport agents: QSS Sender Score Agent and QSS URL Blocklist Agent. Other third-party solutions may provide additional transport agents for Exchange. These are shown in the Third-Party Transport Agents section in QSS Exchange Anti-Spam Toolkit.
The Transport Agents page in QSS Exchange Anti-Spam Toolkit allows all transport agents in Exchange to be managed, not just anti-spam transport agents.
For more information about Transport Agents, see Transport agents in Exchange Server.
For instructions on how to install the anti-spam transport agents, see Installing Exchange Anti-Spam Transport Agents .
Service Restart Required
The Microsoft Exchange Transport Service must be restarted after installing, enabling or disabling any transport agents, or after modifying the priority of any transport agents. If any modified Transport Agents are installed on the Front-End Transport Service (see below), the Microsoft Exchange Frontend Transport Service must also be restarted.
Both of these services can be restarted from the Transport Agents page in QSS Exchange Anti-Spam Toolkit.
Adding a Transport Agent
A transport agent can be manually added by clicking the Add Transport Agent button. You will need the technical details of the transport agent, including the Transport Agent Factory Type and the assembly path. These must be provided by the developer of the transport agent. For technical details of built-in transport agents, and QSS Exchange Anti-Spam Toolkit anti-spam agents are provided for reference, see Installing Exchange Anti-Spam Transport Agents.
Modifying or Deleting a Transport Agent
Once a transport agent has been installed, it can be enabled or disabled, and the priority (order) can be changed by clicking on the name of the transport agent. To modify any any other properties of a transport agent it is necessary to delete and re-add it. QSS Exchange Anti-Spam toolkit only allows modification or deletion of third-party (not system or built-in) transport agents. Modification of the priority of system transport agents is possible with PowerShell commands; see Recommended Transport Agent Priority Order.
Exercise Caution with Manual Installation of Transport Agents
While possible, manual addition of the QSS Anti-Spam Toolkit Agents is not recommended and should only be performed in consultation with Quantum Software Solutions support. The provided scripts should be used to install both the built-in anti-spam agents and the QSS Exchange Anti-Spam Toolkit additional agents. Manual installation of transport agents carries a high risk of error and should only be used in special circumstances.
It should be noted that incorrect installation of transport agents can impact the Exchange server message pipeline to the point of preventing the server from receiving mail and crashing the Microsoft Exchange Transport or Microsoft Exchange Frontend Transport services.
Do Not Manually Delete and Re-Install Transport Agents
Manual deletion or installation of any System (built-in) Transport Agents or any Quantum Software Solutions transport agents is not covered by Quantum Software Solutions support, except in very specific circumstances. The installer or provided scripts should always be used, except under the guidance of Quantum Software Solutions support.
The only reasons to delete and re-install any transport agent would be if the installation details (Assembly Path or Transport Agent Factory Type) are incorrect, or if the agent needs to be installed on a different Transport Service (Hub or Front-End).
If a transport agent shows as installed and enabled, and its technical details are verified as correct, manual deletion and re-installation of that transport agent offers no value and is specifically NOT recommended as a troubleshooting step.
Restarting the Microsoft Exchange Transport and/or Microsoft Exchange Frontend Transport service will reload and restart all transport agents. Even if the assembly (file) of a transport agent is over-written, a service restart will load the new assembly.
If you must delete or install a transport agent manually, it is absolutely imperative that the Transport Agent Name, Assembly Path and Transport Agent Factory Type are copied to the clipboard before deletion (to keep an accurate record of the existing configuration). During installation, the details must be pasted from a known accurate source (such as this documentation) during re-installation. Support requests found to have been caused by typos in manual transport agent installation will incur a charge.
Hub & Front-End Transport Service
Exchange Transport Agents can be installed on either the Hub or the Front-End Transport service. By default, transport agents are installed on the Hub service.
- In an environment without Edge Transport Servers, we recommend installing all transport agents on the Hub Transport service (even though it is possible to use the Front-End Transport service on Hub servers). The script included with QSS Exchange Anti-Spam Toolkit installs all of the built-in anti-spam agents on the Hub Transport service.
- In an environment with Edge Transport servers, we recommend installing all of the agents on the Front-End Transport service on the Edge Transport servers. In this scenario, it is not normally necessary to install any agents on the Mailbox (Hub) servers. The built-in Exchange Script can be used to install the built-in anti-spam agents on the Front-End Transport service.