C# 发送邮件问题

 阿里云服务25端口不开放解决方案

要用System.Web.Mail，之所以不行，是因为System.Net.Mail，中SmtpClient只支持Explicit SSL但是不支持Implicit SSL，而扩展SSl的SMTP会话是起于未加密的通道即加密的25端口，然后使用SSL切换到安全通信465，如果你的服务器禁用25，扩展ssl开始都没办法开始。所以发不出去，所以用SmtpClient行不通，而已改用System.Web.Mail。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Web.Mail;

namespace Demo
{
    /// <summary>
    /// 要用System.Web.Mail，之所以不行，是因为System.Net.Mail，中SmtpClient只支持Explicit SSL但是不支持Implicit SSL，而扩展SSl的SMTP会话是起于未加密的通道即加密的25端口，然后使用SSL切换到安全通信465，如果你的服务器禁用25，扩展ssl开始都没办法开始。所以发不出去，所以用SmtpClient行不通，而已改用System.Web.Mail。 
    /// MailToolSSL mail = new MailToolSSL("smtp.163.com", "password", "", "*****@163.com");
    /// mail.CreateMail("1596782257@qq.com", "", "", "测试主题", "内容--人生得意须尽欢", "HTML", true);
    /// mail.SendMail();
    /// </summary>
    public class MailToolSSL
    {
        public MailMessage _MailMessage;

        public int _SenderPort = 465; //端口
        public string _SenderServerHost; //smtp.163.com
        public string _SenderPassword; //密码
        public string _SenderUsername; //
        public string _SenderMail; //*****@163.com
        public bool _EnableSsl = true; //SSL

        public MailToolSSL(string SenderServerHost, string SenderPassword, string SenderUsername, string SenderMail)
        {
            this._SenderServerHost = SenderServerHost;
            this._SenderPassword = SenderPassword;
            this._SenderUsername = SenderUsername;
            this._SenderMail = SenderMail;
        }

        /// <summary>
        /// 创建Mail
        /// </summary>
        /// <param name="recipient">收件人</param>
        /// <param name="cc">CC</param>
        /// <param name="bcc">BCC</param>
        /// <param name="subject">标题</param>
        /// <param name="content">内容</param>
        /// <param name="format">格式</param>
        /// <param name="sslEnable"></param>
        public ReturnResults CreateMail(string recipient, string cc, string bcc, string subject, string content, string format, bool sslEnable)
        {
            try
            {
                _MailMessage = new MailMessage();
                _MailMessage.To=recipient;
                _MailMessage.From = _SenderMail;
                if (!string.IsNullOrEmpty(cc))
                    _MailMessage.Cc = cc;
                if (!string.IsNullOrEmpty(bcc))
                    _MailMessage.Bcc = bcc;
                _MailMessage.Subject = subject;
                _MailMessage.Body = content;
                if (format.ToUpper().Equals("HTML"))
                    _MailMessage.BodyFormat = System.Web.Mail.MailFormat.Html;
                else
                    _MailMessage.BodyFormat = System.Web.Mail.MailFormat.Text;
                    _MailMessage.BodyEncoding = System.Text.Encoding.UTF8;
                _MailMessage.Priority = MailPriority.Normal;
                _EnableSsl = sslEnable;
                return ReturnResults.Success("Mail创建成功");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
                return ReturnResults.Error("Create Mail 异常" + ex.ToString());
            }           
        }

        public ReturnResults SendMail()
        {
            try
            {
                if (_MailMessage != null)
                {
                    _MailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1"); //身份验证  
                    _MailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", _MailMessage.From); //邮箱登录账号  
                    _MailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", _SenderPassword); //登录密码  
                    _MailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserverport", 465);//端口  
                    _MailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpusessl", "true");//SSL加密  
                    System.Web.Mail.SmtpMail.SmtpServer = _SenderServerHost; //smtp.163.com
                    System.Web.Mail.SmtpMail.Send(_MailMessage);
                    return ReturnResults.Success("Mail发送成功");
                }
                return ReturnResults.Error("创建的Mail为空 ,检查CreateMail 方法");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
                return ReturnResults.Error("Mail发送异常" + ex.ToString());
            }
        }
        public class ReturnResults
        {
            public bool state { get; set; }
            public string msg { get; set; }
            private ReturnResults(bool _state, string _msg)
            {
                this.state = _state;
                this.msg = _msg;
            }

            public static ReturnResults Success(String msg)
            {
                return new ReturnResults(true, msg);
            }
            public static ReturnResults Error(String msg)
            {
                return new ReturnResults(false, msg);
            }

            public static ReturnResults Anything(bool state, String msg)
            {
                return new ReturnResults(state, msg);
            }
        }
    }
}