支持ESMTP身份验证的邮件发送

使用.NET Framework下的System.Net.Mail.SmtpClient可以很容易的实现邮件发送，但现在很多邮件服务器已经支持ESMTP协议。而ESMTP最大的区别在于发送时需要提供帐号密码做验证。ESMTP通过流的方式发送命令与服务器交互，完成邮件的发送与接受。更多关于SMTP的命令请参考：http://www.magicwinmail.com/technic_smtp.php

下面是一个简单的示例：(没有做任何判断与封装，仅供参考)

string smtp ="mail.com";
        string from ="send@mail.com";
        string pwd ="pwd";
        string to ="rec@mail.com";

        //建立链接
        TcpClient tc =new TcpClient(smtp,25);
        byte[] b =newbyte[1024];
        tc.GetStream().Read(b,0,b.Length);
        Response.Write(Encoding.UTF8.GetString(b)+"<br/>");

        //标识身份
        WriteMsg(tc.GetStream(), "HELO xxxx\r\n");
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //身份验证开始
        WriteMsg(tc.GetStream(), "AUTH LOGIN\r\n");
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //帐号 base64编码
byte[] bTxt=newbyte[1024];
        bTxt=Encoding.UTF8.GetBytes(from);
        WriteMsg(tc.GetStream(), Convert.ToBase64String(bTxt)+"\r\n");
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //密码base64编码
        bTxt=Encoding.UTF8.GetBytes(pwd);
        WriteMsg(tc.GetStream(), Convert.ToBase64String(bTxt) +"\r\n");
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");
        //身份验证结束
        
        //发送邮件地址
        WriteMsg(tc.GetStream(), string.Format("MAIL FROM:{0}\r\n", from));
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //接受邮件地址,可以有多个RCPT TO
        WriteMsg(tc.GetStream(), string.Format("RCPT TO:{0}\r\n", to));
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //初如化
        WriteMsg(tc.GetStream(), "DATA \r\n");
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //邮件内容
        StringBuilder sb =new StringBuilder();
        sb.AppendFormat("From:{0}\r\n", from);//发信人
        sb.AppendFormat("To:{0}\r\n", to);//收信人,可以有多个,用分号隔开, 这两行可以与上面的MAIL FROM和RCPT TO不同(显示在邮件内容里的)
        sb.AppendFormat("Date:{0}\r\n",DateTime.Now.ToString());//时间
        sb.AppendFormat("Subject:{0}\r\n", "测试");//主题
        sb.Append("\r\n");
        sb.Append("内容"); //正文
        sb.Append("\r\n.\r\n");

        WriteMsg(tc.GetStream(), sb.ToString());
        Response.Write(ReadMsg(tc.GetStream()) +"<br/>");

        //结束会话
        WriteMsg(tc.GetStream(), "QUIT");
        
        //关闭链接
        tc.Close(); 

privatevoid WriteMsg(NetworkStream ns,string msg)
    {
        byte[] bw = Encoding.UTF8.GetBytes(msg);
        ns.Write(bw,0,bw.Length);
    }
    privatestring ReadMsg(NetworkStream ns)
    {
        byte[] br =newbyte[1024];
        ns.Read(br,0,br.Length);
        return Encoding.UTF8.GetString(br);
    }

如果运行正常，上面的返回状态依次为：

220 mail.com ESMTP CMailServer 5.4.6 SMTP Service Ready
250 welcome here 
334 VXNlcm5hbWU6 
334 UGFzc3dvcmQ6 
235 OK 
250 OK 
250 OK 
354 send the mail data, end with . 
250 OK 

主要还是要熟悉SMTP协议及相关命令，按其格式发送数据与服务端交互。注意命令中间的space(空格)及结尾处的CRLF(回车换行)。

标签：SMTP,ESMTP,Email,发邮件,身份验证
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