I was using `SMTPClient.Send(mail)` method to send emails, but then I saw, if the email id is not present (does not exists), my application waits till it receives the exception and then allows user to perform further tasks.

So I thought of using SMTPClient.SendAsync Method.

My doubt!! Where can this userToken Object be used which is passed as the parameter to the method? I searched many things online but din't find a good example. Even in [MSDN](http://msdn.microsoft.com/en-us/library/x5x13z6h.aspx#snippetGroup) they use it like this

```
string userState = "test message1";
client.SendAsync(message, userState);

```

But then what can it be really used for?

Thank you in advance.