System.Net.Mail 发送邮件时，身份认证失败的问题

节日将至，需要写一个托盘程序，定时发送邮件至客户邮箱
于是架了一个CMail服务器，建立了一个用户post@5liao.cc

开始写程序

代码

        static string sendMail(string to, string title, string content)
        {
            string strHost = "xxx.xxx.xxx.x";   //STMP服务器地址
            string strAccount = "post@5liao.cc";       //SMTP服务帐号
            string strPwd = "1122333";       //SMTP服务密码
            string strFrom = "post@5liao.cc";  //发送方邮件地址



            SmtpClient _smtpClient = new SmtpClient();
            _smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;//指定电子邮件发送方式
            _smtpClient.Host = strHost; ;//指定SMTP服务器
            _smtpClient.Credentials = new System.Net.NetworkCredential(strAccount, strPwd);//用户名和密码

            MailMessage _mailMessage = new MailMessage(strFrom, to);
            _mailMessage.Subject = title;//主题
            _mailMessage.Body = content;//内容
            _mailMessage.BodyEncoding = System.Text.Encoding.UTF8;//正文编码
            _mailMessage.IsBodyHtml = true;//设置为HTML格式
            _mailMessage.Priority = MailPriority.High;//优先级

            try
            {
                _smtpClient.Send(_mailMessage);
                return "发送成功";
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }

本以为很简单，调用上面方法后，却总是提示“身份认证失败”。

郁闷了，换成搜狐邮箱后发送成功。于是考虑是服务器配置问题。关防火墙，关杀毒软件，关CMail的ESMTP仍然无效（应该是ESMTP的问题）。

网上搜索资料。改用System.Web.Mail后发送成功

(因是winform，需要对System.Web进行引用)

代码

static string sendMail(string to,string title,string content)
        {
            System.Web.Mail.MailMessage _mailMessage = new System.Web.Mail.MailMessage();
            _mailMessage.Body = content;
            _mailMessage.From = "post@5liao.cc";
            _mailMessage.Subject = title;
            _mailMessage.To = to;
            _mailMessage.BodyEncoding = System.Text.Encoding.UTF8;
            _mailMessage.BodyFormat = MailFormat.Html;
            _mailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", 1);
            _mailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", "post@5liao.cc");
            _mailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", "******"); 
            System.Web.Mail.SmtpMail.SmtpServer = "XXx.xxx.xxx.x"; 
            try
            {
                System.Web.Mail.SmtpMail.Send(_mailMessage);
                return "发送成功";
            }
            catch(Exception ex)
            {
                return ex.Message;
            }
        }