How to intercept mail messages on a POP3 server

I need an application that will intercept all incoming mail messages and modify them 开发者_JAVA百科according to some specs. I am an absolute rookie at this, please detail :)

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Try this sample code

Dim _tcpClient As New TcpClient
Dim _networkStream As NetworkStream
Dim _Msg As String
With _tcpClient
    .Connect(Me.txtServerIp.Text, Integer.Parse(Me.txtPortNum.Text))
    _networkStream = .GetStream
    Dim sw As New StreamWriter(_networkStream)
    Dim sr As New StreamReader(_networkStream)
    If Not CheckError(sr.ReadLine()) Then
        sw.WriteLine(String.Format("USER {0}", Me.txtUsername.Text))
        sw.Flush()
    End If

    If Not CheckError(sr.ReadLine()) Then
        sw.WriteLine(String.Format("PASS {0}", Me.txtPassword.Text))
        sw.Flush()
    End If

    If Not CheckError(sr.ReadLine()) Then
        sw.WriteLine("STAT ")
        sw.Flush()
    End If
    _Msg = sr.ReadLine
    Dim MsgCount As String = _Msg.Split(New String() {" "},  _
        StringSplitOptions.RemoveEmptyEntries)(1)
    If Integer.Parse(Me.lblMsgCount.Text) < Integer.Parse(MsgCount) Then
        Me.lblMsgCount.Text = MsgCount
    End If
    sw.WriteLine("Quit ")
    sw.Flush()
    sw.Close()
    sr.Close()
    _networkStream.Close()
    _tcpClient.Close()
End With

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All incoming messages will be coming on over SMTP.

So, you need to do 1 of 2 things:

1. If your current server supports it, hook into it's SMTP events, and modify the message before it is passed on to the local intended user.

   or

2. You will need a SMTP proxy service, that sits in front of your real SMTP server.

Inside of the SMTP proxy, modify the message, and pass it on to your real SMTP server.