C#'无法访问已释放的对象。对象名称:“SslStream”。'

public static List<Message> FetchAllMessages(string hostname, int port, string username, string password, string proxyIp, int proxyPort)
{
    // The client disconnects from the server when being disposed
    using (Pop3Client client = new Pop3Client())
    {
        var proxyClient = new HttpProxyClient(proxyIp, proxyPort);
        using (var sslStream = new SslStream(proxyClient.CreateConnection(hostname, port).GetStream()))
        {
            sslStream.AuthenticateAsClient(hostname);
            client.Connect(sslStream);
            // Authenticate ourselves towards the server
            client.Authenticate(username, password);
            // Get the number of messages in the inbox
            int messageCount = client.GetMessageCount();

            // We want to download all messages
            List<Message> allMessages = new List<Message>(messageCount);

            // Messages are numbered in the interval: [1, messageCount]
            // Ergo: message numbers are 1-based.
            // Most servers give the latest message the highest number
            for (int i = messageCount; i > 0; i--)
            {
                allMessages.Add(client.GetMessage(i));
            }
                            // Now return the fetched messages
            return allMessages;
        }
    }
}

更新:

在returnallmessages上放置一个断点;如果将其悬停在sslStream对象上,则不会释放它。