Windows application gets stuck while using workflow

You do not want to use a separate process - you want to use a different thread.

, . , .

, , BackgroundWorker. , Control.Invoke Control.BeginInvoke . , , - , , , ( , BackgroundWorker ), EDIT: BackgroundWorker , .

- :

public void SendEmailButtonClicked(object sender, EventArgs e)
{
    // Make any changes to the UI here to disable whatever you want
    new Thread(SendEmail).Start();
}

private void SendEmail()
{
    // Do the sending of the email here (this is in the non-UI thread)

    // Then afterwards, possibly in a finally block
    Action action = EmailSent;
    this.BeginInvoke(action);
}

private void EmailSent()
{
    // Back in the UI thread, do whatever you need to indicate
    // success/failure, re-enable disabled parts of the UI etc
}