Smtp-Auth機能を使用してのメール送信

string to = "送信元";
string from = "送信先";
string subject = "テスト";
string body = "テストです。";

MailMessage message = new MailMessage(from, to, subject, body);
message.BodyEncoding = Encoding.GetEncoding("iso-2022-jp");
SmtpClient client = new SmtpClient("SMTPサーバ",587);
client.Credentials = new NetworkCredential("送信元のメール名称", "パスワード");
client.EnableSsl = false;
//client.UseDefaultCredentials = true;  
client.Timeout = 10000;
client.Send(message);