Operation not allowed on non-connected sockets

[Domgrar]

Hi I'm trying to create a tcp-server and running into issues getting the message "The operation is not allowed on non-connected sockets"

The project is an AvaloniaUI project...when I create my MainWindow I start up a TcpListener and run it on a background thread

private TcpListener _listener;
        public MainWindow()
        {
            InitializeComponent();
            DataContext = _vm;
 
 
            _listener = new TcpListener(IPAddress.Any, 1025);
            _listener.Start();
            Thread smtpThread = new Thread(StartSmtpLocal);
            smtpThread.IsBackground = true;
            smtpThread.Start();
 
        }

StartSmtpLocal looks like

void StartSmtpLocal()
        {
                while (true)
                {
                    Console.WriteLine("Waiting for connection...");
                    TcpClient client = _listener.AcceptTcpClient();
                    SMTPServer handler = new SMTPServer();
 
                    handlers.Add(handler); 
                    handler.Initialize(client, SmtpMessageComplete);
                    Thread thread = new Thread(handler.Run);
                    // thread.IsBackground = true;
                    thread.Start();
                } 
        }

SmtpServer -

public class SMTPServer
    {
        private TcpClient _client;
        private Action<MimeMessage> _finishAction;
        private MimeMessage _messageRead;
        public void Initialize(TcpClient client, Action<MimeMessage> finishAction)
        {
            _client = client;
            _finishAction = finishAction;
        }
 
        public void Run()
        {
            Write("220 localhost -- Fake proxy server");
            // string message = String.Empty;
            // MimeMessage message;
            string message;
 
            while (true)
            {
                message = Read();
                // message = Read();
 
                if (message.Length > 0)
                {
                    if (message.StartsWith("QUIT"))
                    {
                        Console.WriteLine("Closing TCP Client");
                        _client.Close();
                        break;
                    }
                    if (message.StartsWith("EHLO"))
                    {
                        Write("250 OK");
                    }
 
                    if (message.StartsWith("RCPT TO"))
                    {
                        Write("250 OK");
                    }
 
                    if (message.StartsWith("MAIL FROM"))
                    {
 
                        Write("250 OK");
                    }
 
                    if (message.StartsWith("DATA"))
                    {
                        Write("354 Start mail input; end with");
                        string msg = Read();
                        MemoryStream stream = new MemoryStream();
                        using (StreamWriter writer = new StreamWriter(stream))
                        {
                            writer.Write(msg);
                            writer.Flush();
                            stream.Position = 0;
 
                            // https://github.com/jstedfast/MimeKit
                            _messageRead = MimeMessage.Load(stream);
                            Console.WriteLine();
                        }
 
                        stream.Close();
 
                        Console.WriteLine();
                        Console.WriteLine($"Message from client {message}");
                        Write("250 OK");
                    }
                }
            }
            Console.WriteLine("Invoking finish action");
            _finishAction.Invoke(_messageRead);
        }
 
        private void Write(string message)
        {
            using (NetworkStream clientStream = _client.GetStream())
            {
                ASCIIEncoding encoder = new ASCIIEncoding();
                byte[] buffer = encoder.GetBytes(message + "\r\n");
 
                clientStream.Write(buffer, 0, buffer.Length);
                clientStream.Flush();
            }
            // NetworkStream clientStream = _client.GetStream();
        }
 
        private string Read()
        {
            byte[] messageBytes = new byte[8192];
            int bytesRead = 0;
            NetworkStream clientStream = _client.GetStream();
            ASCIIEncoding encoder = new ASCIIEncoding();
            bytesRead = clientStream.Read(messageBytes, 0, 8192);
            string strMessage = encoder.GetString(messageBytes, 0, bytesRead);
            return strMessage;
        }
 

Line 93 in SmtpServer is where the error is happening

I have no idea what is causing the Client to disconnect so quickly after it's accepted. Any guidance in the right direction is greatly appreciated!