使用微软邮箱发送邮件

 System.Net.Mail.MailMessage mailMessage = new System.Net.Mail.MailMessage();
 mailMessage.From = new MailAddress("123456@hotmail.com", "**********", Encoding.UTF8);
 mailMessage.To.Add(new MailAddress("*****@126.com"));

 mailMessage.Subject = "Test";
 mailMessage.Body = "FYI";
 mailMessage.IsBodyHtml = true;
 mailMessage.BodyEncoding = System.Text.Encoding.UTF8;
 mailMessage.Priority = System.Net.Mail.MailPriority.Normal;

 System.Net.Mail.SmtpClient smtp = new SmtpClient();
 smtp.Host = "smtp.live.com";
 smtp.Port = 587;
 smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
 smtp.Timeout = 1000 * 60 * 30;
 smtp.UseDefaultCredentials = false;

   //解决异常: The server response was: 5.7.3 Requested action aborted; user not authenticated
   //chjuqegazuwyznmc 不是邮箱密码，而是微软帐户提供的app password，需要自己配置生成。
   //如果使用邮箱密码，会被认为发送垃圾邮件，而被锁定账号。
   smtp.EnableSsl = true;
   smtp.Credentials = new System.Net.NetworkCredential("123456@hotmail.com", "chjuqegazuwyznmc");

   //解决异常: The remote certificate is invalid according to the validation procedure.

 ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate,

            X509Chain chain, SslPolicyErrors sslPolicyErrors)
            { return true; };

 smtp.Send(mailMessage);

配置生成 app password: