How to configure NBug to send email

I have a WPF application that I would like to configure to use NBug to send error reports by email.

The config tool is working correctly and I get a test email, but when I add NBug to the application and run an uncaught exception, I don't get an email. The only configuration I have done follows the Getting Started guide (freely translated to VB.Net).

Private Sub Application_Startup(sender As Object, e As StartupEventArgs) Handles Me.Startup
    AddHandler AppDomain.CurrentDomain.UnhandledException, NBug.Handler.UnhandledException
    AddHandler Application.Current.DispatcherUnhandledException, NBug.Handler.DispatcherUnhandledException
    AddHandler TaskScheduler.UnobservedTaskException, NBug.Handler.UnobservedTaskException

    NBug.Settings.UIMode = NBug.Enums.UIMode.Full
    NBug.Settings.StoragePath = Environment.GetFolderPath(Environment.SpecialFolder.Desktop)
    NBug.Settings.AddDestinationFromConnectionString("Type=Mail;From=bugs@xxx.com;Port=465;SmtpServer=smtp.gmail.com;To=support@xxx.com;UseAttachment=True;UseAuthentication=True;UseSsl=True;Username=bugs@xxx.com;Password=xxx;")
    NBug.Settings.ReleaseMode = True

End Sub

      

        
        
        
      

    

The above code removed the username / password from our gmail account which is used for bug reporting.

Any ideas what is wrong with the config or how I could debug?

A zip file attachment is generated, but no email is sent.