c smtpclient谷歌邮件垃圾邮件文件夹

我发送了一封简单的电子邮件,但它会进入谷歌邮件的垃圾邮件文件夹。其他电子邮件帐户不是这样。有什么想法吗?

   MailMessage Email = new MailMessage();
   Email.SubjectEncoding = Encoding.UTF8;
   Email.BodyEncoding = Encoding.UTF8;
   Email.From = new MailAddress(appSettings.MailSender);
   Email.To.Add(empfaenger);
   Email.Subject = "mytitle";
   Email.Body = "Plaintext";
   Email.IsBodyHtml = false;

   SmtpClient MailClient = new SmtpClient(appSettings.MailServer,25);
   MailClient.Timeout = 300000;
   MailClient.EnableSsl = true;
   MailClient.Credentials = new System.Net.NetworkCredential(appSettings.MailUser, appSettings.MailPass);
   MailClient.SendAsync(Email, null);