我真的被大家搞亂了，還真的以為BAT無所不能.....(PS1還不錯無所不能)
真的不要用BAT/PS1啦，一點秘密也沒有，郵箱帳號密碼用記事本就可以直接看光光

以下是我用C# (Net FrameWork 4.7.2)寫的範例

!!!! 我沒說C#編譯出來的EXE不能反組譯哦，只是需要一點小功夫，至少不是記事本 !!!!

using System;
using System.Net;
using System.Net.Mail;
using System.Text;

namespace SendMailSMTPs
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SmtpClient smtpClient = new SmtpClient())
            {
                System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(RemoteServerCertificateValidationCallback);

                var basicCredential = new NetworkCredential("MIS", "594088");
                
                smtpClient.Port = 465; //使用SMTPS 465端口
                smtpClient.EnableSsl = true;  // 如果主機支援SSL的話
                smtpClient.Host = "mail.yourCompany.com.tw";
                smtpClient.UseDefaultCredentials = false; //不使用匿名帳戶
                smtpClient.Credentials = basicCredential; // 上上上上上那一行的帳密
                using (MailMessage message = new MailMessage())
                { // 信件內容
                    //發信者的郵箱跟名稱，以下全用utf-8避免亂碼
                    MailAddress fromAddress = new MailAddress("mis@mail.yourCompany.com.tw", "MIS群發", Encoding.GetEncoding("utf-8")); 
                    message.SubjectEncoding = Encoding.GetEncoding("utf-8");
                    message.BodyEncoding = Encoding.GetEncoding("utf-8");
                    message.From = fromAddress;
                    message.Subject = "測試郵件";
                    message.SubjectEncoding = Encoding.GetEncoding("utf-8");
                    message.IsBodyHtml = true; // 如果不使用HTML的話可以不用設
                    message.Body = $"信件內容......<H1>支援HTML格式</H1>";
                    message.BodyEncoding = Encoding.GetEncoding("utf-8");
                    message.To.Add(new MailAddress("mydarling@mail.hisCompany.com.tw", "", Encoding.GetEncoding("utf-8")));
                    // 另一個收件者
                    message.To.Add(new MailAddress("mydarling2@gmail.com","親愛的GMAIL",Encoding.GetEncoding("utf-8")));
                    //CC、BCC也是比照辦理 
                    //message.CC.Add(...  message.BCC.Add
                    try
                    {
                            // 送出......
                            smtpClient.Send(message);
                    }
                    catch (Exception ex)
                    {
                        // 錯誤處理
                        Console.WriteLine(ex.Message);
                    }
                }

            }
        }
        static private bool RemoteServerCertificateValidationCallback(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors sslPolicyErrors)
        {
            Console.WriteLine(certificate);
            return true;
        }
    }
}

我用OUTLOOK正確收到信了

GMAIL(而且沒被丟進垃圾信件去)

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