"QQEmailConfig": {
     //发件人
    "From": {
      "email": "自己的QQ邮箱",
      "displayname": "tomorrow得到系统通知"//显示的名称
    },
    "AuthorizationCode": "自己的授权码",
    //收件人
    "Addressee": [
      {
        "email": "张三的QQ邮箱",
        "displayname": "张三"
      },
      {
        "email": "李四的QQ邮箱",
        "displayname": "李四"
      }
    ],
    "Subject": "tomorrow的系统通知123",//统一标题
    "Host": "smtp.qq.com",//主机
    "Port": 587,//端口
    "EnableSsl": true  //是否加密

  },

 public class EmailConfig
    {
        public class Config
        {
            public string email { get; set; }
            public string displayname { get; set; }
        }
        public Config From { get; set; }
        public Config[] Addressee { get; set; }
        public string AuthorizationCode { get; set; }
        public string Subject { get; set; }
        public string Host { get; set; }
        public int Port { get; set; }
        public bool EnableSsl { get; set; }

    }

public async Task<IActionResult> SendQQEmail()
        {
            //读取配置文件
            EmailConfig emailConfig = _configuration.GetSection("QQEmailConfig").Get<EmailConfig>();
            //实例化对象
            using(MailMessage mail=new MailMessage())
            {
                //发件人
                mail.From = new MailAddress(emailConfig.From.email, emailConfig.From.displayname);
                //收件人
                foreach (var item in emailConfig.Addressee)
                {
                    mail.To.Add(new MailAddress(item.email, item.displayname));
                }
                //标题
                mail.Subject = emailConfig.Subject;
                //内容
                mail.Body = "<b>我变了</b>没有变";
                //内容是否为html渲染
                mail.IsBodyHtml = true;
                //标题编码
                mail.SubjectEncoding = Encoding.UTF8;
                //内容编码
                mail.BodyEncoding = Encoding.UTF8;
                //附件
                mail.Attachments.Add(new Attachment(@"C:\Users\Administrator\Pictures\Saved Pictures\timg.jpg")); 
                //smtp客户端
                using(SmtpClient client=new SmtpClient())
                {
                    //主机
                    client.Host = emailConfig.Host;
                    //端口
                    client.Port = emailConfig.Port;
                    //凭证（发件人email 授权）
                    client.Credentials = new NetworkCredential(emailConfig.From.email, emailConfig.AuthorizationCode);
                    //是否加密
                    client.EnableSsl = emailConfig.EnableSsl;
                    //发送邮件
                    await client.SendMailAsync(mail);
                }
            };
            return new JsonResult(new
            {
                Code=200,
                message="邮件完成，请注意查收",
                data = emailConfig.Addressee
            });
        }