Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.IO
Imports System.Threading
 
 
Public Class Form1
    Private stream As NetworkStream
    Private client As New TcpClient
 
    Private Sub cmdPOPen_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Me.Load
        Dim server As String = "pop.test.de"
        Dim user As String = "test"
        Dim password As String = "test123"
 
        client.Connect(server, 110)
        stream = client.GetStream()
 
        Dim response As String()
 
        readResponse()
        sendCommand("USER " + user)
        sendCommand("PASS " + password)
        response = sendCommand("STAT").Split(" ")
        For i As UShort = 1 To response(1)
            Dim message As String = getMessage("RETR " & i)
            Using sr As New StreamWriter("C:\Testordner_" & i & ".txt")
                sr.Write(message)
            End Using
        Next
        txtResponse.Text += sendCommand("QUIT")
    End Sub
 
    Private Function sendCommand(ByVal command As String) As String
        Dim data As Byte() = Encoding.ASCII.GetBytes(command & vbCrLf)
 
        If stream.DataAvailable Then
            Dim sr As New StreamReader(stream)
            Do While stream.DataAvailable
                sr.ReadLine()
            Loop
        End If
 
        'senden
        stream.Write(data, 0, data.Length)
 
        Return readResponse()
    End Function
 
    Private Function readResponse() As String
        Dim response As String = ""
        Dim buffer As New StringBuilder
        Dim sr As New StreamReader(stream)
 
        'auf Daten warten
        Do Until stream.DataAvailable
            Thread.Sleep(100)
        Loop
        'Daten lesen
        Do While stream.DataAvailable
            Thread.Sleep(50)
            buffer.Append(sr.ReadLine + vbCrLf)
        Loop
 
        'Logging
        txtResponse.Text += buffer.ToString
 
        Return buffer.ToString
    End Function
 
    Private Function getMessage(ByVal command As String) As String
        Dim data As Byte() = Encoding.ASCII.GetBytes(command & vbCrLf)
        Dim response As String = ""
        Dim buffer As New StringBuilder
        Dim sr As New StreamReader(stream)
 
        stream.Write(data, 0, data.Length)
 
        Do Until stream.DataAvailable
            Thread.Sleep(100)
        Loop
        Do Until response = "."
            response = sr.ReadLine
            buffer.Append(response + vbCrLf)
        Loop
 
        Return buffer.ToString
    End Function
 
End Class