The following are the prerequisites that are required for you to implement an agent:

• A computer that is running Exchange 2007 that has the Edge Transport or the Hub Transport server role installed 
  
• Microsoft .NET Framework 2.0 software development kit (SDK) 
  

We also recommend that you install Microsoft Visual Studio .NET 2005.

Requirements for Implementing a Transport Agent

Responding to Transport Events

The following example shows a minimal implementation of classes that derive from the SmtpReceiveAgentFactory and SmtpReceiveAgent classes.

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Exchange.Data.Transport;
using Microsoft.Exchange.Data.Transport.Smtp;

namespace MyAgents
{
    public sealed class MyAgentFactory : SmtpReceiveAgentFactory
    {
        public override SmtpReceiveAgent CreateAgent(SmtpServer server)
        {
            return new MyAgent();
        }
    }
    public class MyAgent : SmtpReceiveAgent
    {
        public MyAgent()
        {
            this.OnEndOfData += new EndOfDataEventHandler(MyEndOfDataHandler);
        }
        private void MyEndOfDataHandler (ReceiveMessageEventSource source, EndOfDataEventArgs e)

        {
            // The following line appends text to the subject of the message that caused the event.
            e.MailItem.Message.Subject += " - this text appended by MyAgent";
        }
    }
}

Imports System
Imports System.Collections.Generic
Imports System.Text
Imports Microsoft.Exchange.Data.Transport
Imports Microsoft.Exchange.Data.Transport.Smtp

Namespace MyAgents

    NotInheritable Class MyAgentFactory
        Inherits SmtpReceiveAgentFactory

        Public Overrides Function CreateAgent(ByVal server as SmtpServer) As SmtpReceiveAgent
            Return New MyAgent
        End Function

    End Class

    Public Class MyAgent
        Inherits SmtpReceiveAgent

        Private Sub MyEndOfHeadersHandler(ByVal source As ReceiveMessageEventSource, ByVal e As EndOfHeadersEventArgs) Handles Me.OnEndOfHeaders
            ' The following line appends text to the subject of the message that caused the event.
            e.MailItem.Message.Subject &= e.MailItem.Message.Subject + " - this text appended by MyAgent"

        End Sub

    End Class

End Namespace

After you compile your agent to a dynamic-link library (DLL), you must install and enable the agent on your development Exchange server. In the Exchange Management Shell, use the Install-TransportAgent command to install your agent, and the Enable-TransportAgent command to enable your agent.

Caution:
Transport agents have full access to all e-mail messages that they encounter. Exchange 2007 does not restrict the behavior of a transport agent. Transport agents that are unstable or that contain security flaws may affect the stability and security of Exchange 2007. Therefore, you must only install transport agents that you fully trust and that have been fully tested.

When you use the Install-TransportAgent cmdlet to install an agent, the Exchange Management Shell keeps a lock on the assembly. To release the lock on the assembly, you must close the instance of the management shell that you used to install the agent. You will be unable to update the assembly until you release the lock.

The following example shows you how to use the Exchange Management Shell to install and enable an agent named MyAgent by using a class derived from SmtpReceiveAgentFactory named MyAgents.MyAgentFactory.

Install-TransportAgent -Name "MyCustomAgent" -TransportAgentFactory "MyAgents.MyAgentFactory" -AssemblyPath "C:\myagents\MyAgent.dll"

This example names the agent MyCustomAgent on the server on which the agent is installed. The following example shows you how to enable the agent named MyCustomAgent.

Enable-TransportAgent -Name "MyCustomAgent"

Concepts