如何保护 在 asp.net 中将发送的电子邮件归类为垃圾邮件

可能的重复项：
如何降低电子邮件的垃圾邮件分数？

我有这个 c# 代码，可以向人们发送大量电子邮件。 但是我发送的电子邮件已被归类为垃圾邮件。我该怎么办 .我应该对我的代码应用任何更改吗？我尝试从sql服务器数据库获取电子邮件地址，我的代码可以附加一个文件。

Entities context = new Entities();
var query = from c in context.Emails select c.EmailAddress;
MailMessage mail = new MailMessage();
Regex sample = new Regex(@"^[-!#$%&'*+/0-9=?A-Z^_a-z{|}~]('.?[-!#$%&'*+/0-9=?A-Z^_a-z{|}~])*
                                  @[a-zA-Z](-?[a-zA-Z0-9])*('.[a-zA-Z](-?[a-zA-Z0-9])*)+$");
int total = 0;//number of all emails
int count = 0;//counter for putting interrupt between each 10 sending
int failed = 0;//number of failed sending
int success = 0;//number of successful sending
double totalsize = 0;//size of attachment file
if (FileUpload1.HasFile)
{
    mail.Attachments.Add(new Attachment(FileUpload1.PostedFile.InputStream, FileUpload1.FileName));
    foreach (Attachment attachment in mail.Attachments)
    {
        string size =attachment.ContentStream.Length.ToString ();
        totalsize=Convert .ToDouble (size);
    }
 }
foreach (var c in query)
{
    if (count == 10)
    {
        Thread.Sleep(10000);
        count = 0;
    }
    mail.From = new MailAddress("hadi@myhost.com");
    mail.Bcc.Add(new MailAddress(c.ToString()));
    mail.Subject = "hello";
    mail.IsBodyHtml = true;
    mail.Body = FCKeditor1.Value.ToString();
    SmtpClient smtp = new SmtpClient();
    smtp.Host = "localhost";
    smtp.Port = 25; 
    if ((sample.IsMatch(c.ToString())) && (sample .IsMatch (mail .From .ToString ())) && (totalsize<1000000))
    {
      try
        {
            smtp.Send(mail);
            //Response.Write("email has sent to " + c.ToString());
            success++;
        }
        catch 
        {
            //Response.Write("email has not sent to " + c.ToString());
            failed++;
        }
        count++;
    }
    total++;
}