Visual Basic

 <br />
Private Enum SMTPResponse As Integer<br />
   CONNECT_SUCCESS = 220<br />
   GENERIC_SUCCESS = 250<br />
   DATA_SUCCESS = 354<br />
   QUIT_SUCCESS = 221<br />
End Enum<br />
<br />
<br />
Public Shared Function IsServerAvailable(ByVal Address As String) As Boolean<br />
            Try<br />
                Dim IPhst As System.Net.IPHostEntry = System.Net.Dns.GetHostEntry(Address)<br />
                Dim endPt As New System.Net.IPEndPoint(IPhst.AddressList(0), 25)<br />
                Dim socket As New System.Net.Sockets.Socket(endPt.AddressFamily, System.Net.Sockets.SocketType.Stream, System.Net.Sockets.ProtocolType.Tcp)<br />
                socket.Connect(endPt)<br />
                If Not CheckResponse(socket, SMTPResponse.CONNECT_SUCCESS) Then<br />
                    socket.Close()<br />
                    Return False<br />
                Else<br />
                    Return True<br />
                End If<br />
            Catch<br />
                Return False<br />
            End Try<br />
        End Function<br />
<br />
Private Shared Function CheckResponse(ByVal Socket As System.Net.Sockets.Socket, ByVal ExpectedResponse As SMTPResponse) As Boolean<br />
            Dim sResponse As String<br />
            Dim iResponse As Integer<br />
            Dim bytes(1024) As Byte<br />
<br />
            While Socket.Available = 0<br />
                System.Threading.Thread.Sleep(100)<br />
            End While<br />
<br />
            Socket.Receive(bytes, 0, Socket.Available, Net.Sockets.SocketFlags.None)<br />
            sResponse = System.Text.Encoding.ASCII.GetString(bytes)<br />
            iResponse = Convert.ToInt32(sResponse.Substring(0, 3))<br />
            If iResponse <> CType(ExpectedResponse, Integer) Then<br />
                Return False<br />
            Else<br />
                Return True<br />
            End If<br />
        End Function<br />