连接sina的smtp发送信体后怎么无回应？

以下是我发的数据：
SendString[0]="EHLO maos\r\n";
SendString[1]="AUTH LOGIN\r\n";
SendString[2]="bWFvczIwMqI=\r\n";//用户名
SendString[3]="MTk4NzA0MDd=\r\n";//密码
SendString[4]="MAIL FROM:<[email protected]>\r\n";
SendString[5]="RCPT TO:<[email protected]>\r\n ";
         SendString[6]="DATA\r\n";
SendString[7]+="From: \"maos\" <[email protected]>\r\n";
SendString[7]+="To: <[email protected]>\r\n";
SendString[7]+="Subject:test!\r\n";
SendString[7]+="Date: Thu, 7 Dec 2006 21:20:12 +0800\r\n";
SendString[7]+="MIME-Version: 1.0\r\n";
SendString[7]+="Content-Type:text/plain;\r\n";
SendString[7]+="charset=\"gb2312\"\r\n";
SendString[7]+="Content-Transfer-Encoding:base64\r\n";
SendString[7]+="X-Priority:3\r\n";
SendString[7]+="X-MSMail-Priority:Normal\r\n";
SendString[7]+="X-Mailer:Microsoft Outlook Express 5.50.4133.2400\r\n";
SendString[7]+="X-MimeOLE:Produced By Microsoft MimeOLE V5.50.4133.2400\r\n\r\n";
SendString[7]+=(CString)finalbase64;
SendString[7]+="\r\n\r\n.\r\n";
SendString[8]="QUIT\r\n";
每次收到服务器回应的“354 End data with <CR><LF>.<CR><LF>”后我发送信体，却得不到回应，是怎么回事？我用的是sina.smtp.com.cn服务器。