Question

I’ve created a small app that watches an inbox using the EWS managed dll.

When I create the StreamingSubscriptionConnection I pass in a 1 minute disconnect.

Then in the on disconnect event handler, I sleep for 45 seconds and reconnect.

If anything is sent to the inbox in the 45 second sleep period, it originally appeared as if it woke up and fired the NotificationEventDelegate properly. However after some testing it appears to fire it multiple times for the same email when more than one email arrives.

If I do not sleep then I don’t have this problem. So my questions are, why would the NotificationEventDelegate not function properly on reconnect, and is there a problem with immediately reconnecting?

my code is as follows,

private MailDirectorServer()
{
    _isRunning = false;

    ExchangeService _service = new ExchangeService()
    {
        Credentials = new WebCredentials(userName, password),
        Url = new Uri(uriAddress)
    };

    _connection = 
        new StreamingSubscriptionConnection(_service, 1);

    // set up subscriptions here.
    _connection.OnNotificationEvent +=
                new StreamingSubscriptionConnection.NotificationEventDelegate(OnNewMail);

    _connection.OnDisconnect +=
        new StreamingSubscriptionConnection.SubscriptionErrorDelegate(OnDisconnect);

    _connection.Open();
    _isRunning = true;
}

private void OnDisconnect(object sender, SubscriptionErrorEventArgs args)
{
    while (true)
    {
        if (_isRunning)
        {
            //_logger.Debug("Sleeping for 45 seconds");
            //Thread.Sleep(new TimeSpan(0, 0, 45));
            _connection.Open();
            _logger.Info("Connection Re Opened");
            break;
        }
        else
        {
            _logger.Info("Closing Down");
            break;
        }
    }
}

Answer 1

Remove the Sleep call – just immediately reconnect (connection.Open). See related SO post. Microsoft also recommends this process of automatic reconnect in their forums.

I would also increase the disconnect interval to 30 minutes to avoid constant opening and closing of the connection. With a one minute disconnect, you may as well be using Pull Subscriptions.

You should also handle the OnSubscriptionError to capture when there are errors with your streaming subscription.