C# SmtpClient 发邮件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Mail;
using System.Net; 
using System.Threading;
using System.IO;
using System.Security.Cryptography;

namespace ConsoleApp348
{
    class Program
    {        
        static string logFullPath = Directory.GetCurrentDirectory() + "\\" + DateTime.Now.ToString("yyyyMMdd") + ".txt";
        static void Main(string[] args)
        {
            Timer emailTimer = new Timer(SendMailCallBack, null, 0, 1);
            Console.ReadLine();
        }
        
        private static void SendMailCallBack(object state)
        {
            string fromMail = "fromMail";
            string fromMailPwd = "fromMailPwd";
            string toMail = "toMail";
            MailExample(fromMail, fromMailPwd, toMail);
        }

        static void MailExample(string fromEmail, string fromEmailPwd, string toEmail)
        {            
            try
            {
                using (SmtpClient smtpClient = new SmtpClient())
                {
                    smtpClient.Host = "smtp.163.com";
                    smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
                    smtpClient.UseDefaultCredentials = false;
                    smtpClient.Credentials = new System.Net.NetworkCredential(fromEmail, fromEmailPwd);
                    using (MailMessage mail = new MailMessage())
                    {
                        mail.BodyEncoding = UTF8Encoding.UTF8;
                        mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
                        mail.From = new MailAddress(fromEmail);
                        mail.To.Add(new MailAddress(toEmail));
                        mail.Subject = $"This is the new test.Now is {DateTime.Now.ToString("mmssffff")}";
                        mail.Body = $"This is the mail body,And now is {DateTime.Now.ToString("yyyyMMddHHmmssffff")}";
                        smtpClient.SendAsync(mail, $"Frommail:{fromEmail},ToMail:{toEmail},send email successfully!");
                        smtpClient.SendCompleted += SmtpClient_SendCompleted;
                    }                        
                }                    
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.StackTrace);
                LogMessage(ex.StackTrace);
            }
        }

        private static void SmtpClient_SendCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
        {
            Console.WriteLine(e.UserState);
            LogMessage(e.UserState.ToString());
        }

        static void LogMessage(string msg)
        {            
            lock(logFullPath)
            {
                using (StreamWriter logWriterStream = new StreamWriter(logFullPath, true, UTF8Encoding.UTF8))
                {
                    logWriterStream.WriteLine($"Log message :{msg},now is {DateTime.Now.ToString("yyyyMMddHHmmssffff")}");
                }
            }           
        }
    }
}

 异步：public void SendAsync(MailMessage message, object userToken);

Sends the specified e-mail message to an SMTP server for delivery. This method  does not block the calling thread and allows the caller to pass an object to  the method that is invoked when the operation completes.