Public Class Client
 
    Private Client As New Net.Sockets.TcpClient
    Private POP3Stream As Net.Sockets.NetworkStream
    Private Connected As Boolean = False
 
    '''<summary>
    '''Verbindungssatus abfragen.
    '''</summary>
    Public ReadOnly Property ConnectionEstablished() As Boolean
 
        Get
            Return Connected
        End Get
 
    End Property
 
    '''<summary>
    '''Nachrichten Klasse
    '''</summary>
    Public Class MessageList
 
        Public ID As Int64
        Public Size As Int64
 
    End Class
 
    '''<summary>
    '''Verfügbarer POP3 Befehlssatz.
    '''</summary>
    Private Class Commands
 
        Public Const Delete As String = "DELE "
        Public Const GetMessage As String = "RETR "
        Public Const List As String = "LIST"
        Public Const Password As String = "PASS "
        Public Const Quit As String = "QUIT"
        Public Const ServerConfirm As String = "+OK"
        Public Const ServerNoMoreData As String = "."
        Public Const User As String = "USER "
 
    End Class
 
    '''<summary>
    '''Stellt die Verbindung zum POP3-Server her.
    '''</summary>
    '''<param name="Server">Servername (subdomain.domain.tld)</param>
    '''<param name="User">Benutzername</param>
    '''<param name="Password">Passwort</param>
    Public Sub Connect(ByVal Server As String, ByVal User As String, ByVal _
      Password As String)
 
        If Connected = True Then Me.Disconnect()
        Try
            Me.Client.Connect(Server, 110)
            Me.POP3Stream = Me.Client.GetStream
            Me.CheckResponse(Me.GetResponse)
            Me.Send(Commands.User + User)
            Me.CheckResponse(Me.GetResponse)
            Me.Send(Commands.Password + Password)
            Me.CheckResponse(Me.GetResponse)
            Me.Connected = True
        Catch ex As Exception
            Me.Disconnect()
            Throw New ApplicationException(ex.Message, ex)
        End Try
 
    End Sub
 
    '''<summary>
    '''Trennt die Verbindung zum POP3-Server her.
    '''</summary>
    Public Sub Disconnect()
 
        If Connected = True Then
            Me.Send(Commands.Quit)
            Me.CheckResponse(Me.GetResponse())
            Me.Connected = False
            Me.Client.Close()
        End If
 
    End Sub