As I explained earlier this property isn't specific to SendMessage method. It configures the amount of time the underlying Socket will wait to receive data.
Here's the code:
using(Smtp smtp = new Smtp())
{
smtp.ReceiveTimeout = TimeSpan.FromSeconds(20);
smtp.Connect("smtp.server.com"); // or ConnectSSL for SSL
smtp.UseBestLogin("user", "password");
smtp.Noop();
smtp.Close();
}