C#发送QQ邮件

/// <summary>
/// 发送邮件
/// </summary>
/// <param name="title">邮箱内容</param>
/// <param name="Email">邮箱地址</param>
/// <param name="value">收件人姓名</param>
/// <returns></returns>
public string Small(string value,string Email,string title)
{
MailMessage mail;
SmtpClient client;
string EmailTitle = "877600684@qq.com";
mail = new MailMessage(EmailTitle,Email);
mail.Body = value;//内容
mail.Subject = title;//标题
mail.IsBodyHtml = true;
mail.SubjectEncoding = System.Text.Encoding.Default;
mail.BodyEncoding = System.Text.Encoding.Default;
//mail.Headers.Add("X-Priority", "3");
//mail.Headers.Add("X-MSMail-Priority", "Normal");
//mail.Headers.Add("X-Mailer", "Microsoft Outlook Express 6.00.2900.2869");
//mail.Headers.Add("X-MimeOLE", "Produced By Microsoft MimeOLE V6.00.2900.2869");
client = new SmtpClient("smtp.qq.com");
client.Credentials = new System.Net.NetworkCredential("用户名", "密码");
//   client.Host = "smtp.qq.com";
//System.Net.NetworkCredential crea = new System.Net.NetworkCredential();
//crea.UserName = "用户名";
//crea.Password = "密码";
System.IO.StreamWriter writer = new System.IO.StreamWriter("D:\\log.txt", true);
try {
client.Send(mail);
//发送成功
writer.WriteLine("邮件发送成功");
writer.Close();
return "0";

}
catch (Exception e)
{
writer.WriteLine("邮件发送失败,错误信息:"+e.ToString());
writer.Close();
return "1";
}
}