Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.io
Imports System.Threading
 
Public stream As NetworkStream
    Public sr As StreamReader
 
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Take.Click
        GetMail("dave.jacobi@igsquerum.de", "dave.jacobi", "***", 1)
    End Sub
 
    Private Function GetMail(ByVal Server As String, ByVal User As String, _
      ByVal Password As String, ByVal Number As 
 
Long) As String
        Dim client As New TcpClient(Server, 110) ' Hier kommt der Fehler*
        stream = client.GetStream()
        sr = New StreamReader(stream)
        txtResponse.Text += sendCommand("?")
        txtResponse.Text += sendCommand("USER " + User)
        txtResponse.Text += sendCommand("PASS " + Password)
        txtResponse.Text += sendCommand("STAT" + vbCrLf)
        txtResponse.Text += sendCommand("RETR " + Number + vbCrLf) 
        txtResponse.Text += sendCommand("QUIT" + vbCrLf)
    End Function
 
    Private Function sendCommand(ByVal send As String) As String
        send += vbCrLf
        Dim data As [Byte]() = Encoding.ASCII.GetBytes(send)
        stream.Write(data, 0, data.Length)
        sr = New StreamReader(stream)
        Dim buffer As New StringBuilder
        Do While sr.Peek() > 0
            Thread.Sleep(100)
            buffer.Append(sr.ReadLine + vbCrLf)
        Loop
        Return buffer.ToString
    End Function