C#邮件发送程序提示错误“551， delivery not allowed to non-local recipient”

Question

请问各位：
    我用C＃写的邮件发送程序，现在总是提示“551， delivery not allowed to non-local recipient”，请问该如何解决？兄弟用的是Socket方式，发送部分代码如下：
try
{
tc=new TcpClient(smtpServer,25);
}
catch (Exception e)
{
tc.Close();
return "network error";
}
ns = tc.GetStream(); string[] SendBuffer;
string SendBufferstr; SendBuffer=new String[4];
SendBuffer[0]="EHLO " + smtpServer + enter;
SendBuffer[1]="AUTH LOGIN" + enter;
SendBuffer[2]=Base64Encode("[email protected]") + enter;
SendBuffer[3]=Base64Encode("abcd") + enter; byte[] WriteBuffer;
WriteBuffer = Encoding.Default.GetBytes(SendBuffer[0]);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong one";

} int StreamSize;
string ReturnValue = String.Empty;
byte[] ReadBuffer = new byte[1024] ;
try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong one";
} if (StreamSize==0)
{
// return "0";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
// return ReturnValue;
} WriteBuffer = Encoding.Default.GetBytes(SendBuffer[1]);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong two";

} try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong two";
} if (StreamSize==0)
{
// return "0";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
// return ReturnValue;
} WriteBuffer = Encoding.Default.GetBytes(SendBuffer[2]);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong three";

} try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong three";
} if (StreamSize==0)
{
// return "0";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
// return ReturnValue;
} WriteBuffer = Encoding.Default.GetBytes(SendBuffer[3]);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong four";

} try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong four";
} if (StreamSize==0)
{
// return "0";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
// return ReturnValue;
} SendBufferstr="MAIL FROM:<" + "[email protected]" + ">" + enter;
WriteBuffer = Encoding.Default.GetBytes(SendBufferstr);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong four";

} try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong four";
} if (StreamSize==0)
{
//                return "0";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
// return ReturnValue;
}

SendBufferstr="RCPT TO:<" + "[email protected]" +">" + enter;
WriteBuffer = Encoding.Default.GetBytes(SendBufferstr);
try
{
ns.Write(WriteBuffer,0,WriteBuffer.Length);
}
catch
{
return "Write wrong four";

} try
{
StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
}
catch
{
return "Read wrong RCPT";
} if (StreamSize==0)
{
return "RCPT";
}
else
{
ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
return ReturnValue;
}

Answer 1

我的邮件程序的Smtp Server是域内的Exchange Server，可以发送域内的邮件，但是发送不了外部邮件。请问如何解决，谢谢！

Answer 2

Smtp服务器指定只能发送域内的邮件，而且这个参数是不能修改的。
可以告诉我发送参数如何指定域吗？谢谢！