private void button1_Click(object sender, EventArgs e)
{
    MessageBox.Show(doValidation("yourAddress@gmail.com"));
}

private string doValidation(string emailAddress)
{
    //Validate to the ultimate level.
    validator1.ValidationLevel = ValidationLevel.SmtpRecipient;

    //Raise the progress event for every validation step.
    validator1.VerboseProgress = true;

    //DNS settings.
    validator1.Dns.Rotateservers = false; //always start with first server
    validator1.Dns.Retries = 2; //try up to 3 times
    validator1.Dns.Timeout = 5000; //5 seconds

    //SMTP settings.
    validator1.Smtp.MailFrom = "from@myDomain.com"; //required
    validator1.Smtp.ConnectTimeout = 40000; //40 seconds
    validator1.Smtp.ReceiveTimeout = 40000; //40 seconds

    //Validate and return the result.
    ValidationState result = validator1.Validate(emailAddress);
    string description = "The validation of " + result.EmailAddress;
    description += " proceeded to the "; + result.Progress.ToString() + " level. ";
    description += (result.Exception == null)
        ? "The validation was successful."
        : "The following exception occurred: " + result.Exception.ToString();
    return description;
}

private void validator1_Progress(object sender, ProgressEventArgs e)
{
    //Record validation progress to a log.
    if (e.ValidationState.Exception == null)
        textLog.AppendText(e.ValidationState.EmailAddress + " OK: " +
            e.ValidationState.Progress.ToString() + Environment.NewLine);
    else
        textLog.AppendText(e.ValidationState.EmailAddress + " ERROR: " +
            e.ValidationState.Exception.Message + Environment.NewLine);
}