Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.io
Imports System.Threading
Public Class GetMail
    Private stream As NetworkStream
    Private sr As StreamReader
    Public server As String = "sender"
    Public user As String = "user"
    Public password As String = "passwort"
    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
    Public Function GetMail(ByVal MailNumber As Integer) As String
        Dim client As New TcpClient(server, 110)
        Dim tmp As New StringBuilder
        stream = client.GetStream()
        sr = New StreamReader(stream)
        With tmp
            .Append(sendCommand("?"))
            .Append(sendCommand("USER " + user))
            .Append(sendCommand("PASS " + password))
            .Append(sendCommand("STAT" + vbCrLf))
            .Append(sendCommand("RETR " + MailNumber.ToString + vbCrLf))
            .Append(sendCommand("QUIT" + vbCrLf))
        End With
        Return tmp.ToString
    End Function
End Class

        Dim m As New GetMail
        m.password = "pass"
        m.user = konto""
        m.server = "pop.server.de"
        Me.RichTextBox1.Text = m.GetMail(2)