C#邮件发送程序提示错误“551， delivery not allowed to non-local recipient”
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( "test@test.com ") + 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: < " + "bluehale@21cn.com " + "> " + 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: < " + "bluehale@emails.bjut.edu.cn " + "> " + 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;
}

[解决办法]
这个可能跟邮箱服务器设置有关系
发送的参数好像能指定域 你可以尝试一下