那位知道SMTP协议命令原始码及工作原理?请多多指教。(50分)

//SMTP_VC.CPP 
#include "stdafx.h" 
#include <winsock2.h> 
#include <string.h> 
#include <stdio.h> 
char szhost[17]="211.150.96.25"; 
//char szhost[17]="127.0.0.1"; 
char szMessage[1024]; 

int checkreturn(char *_msg); 
int postcmd(SOCKET smtp,char * cmd,char * ret,bool rec); 
int base64enc(char *,char *); 

int main(HINSTANCE hInstance, 
HINSTANCE hPrevInstance, 
LPSTR lpCmdLine, 
int nCmdShow) 
{ 
// printf("%s",lpCmdLine); 
//MessageBox(0,lpCmdLine,"jk",MB_OK); 
WSADATA wsd; 
SOCKET smtp; 
int ret; 
sockaddr_in server; 
hostent *host=NULL; 
char cmd[100]; 
if (WSAStartup(MAKEWORD(2,2),&wsd)!=0) //初始化 
{ 
MessageBox(0,"错误1","错误",MB_OK); 
return 1; 
} 

smtp=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP); 
if (smtp==INVALID_SOCKET) 
{ 
MessageBox(0,"错误2","错误",MB_OK); 
return 2; 
} 

server.sin_family=AF_INET; 
server.sin_port=htons(25); 
server.sin_addr.s_addr=inet_addr(szhost); 
if(connect(smtp,(struct sockaddr*)&server,sizeof(server))==SOCKET_ERROR) 
{ 
//MessageBox(0,"连接错误","错误",MB_OK); 
printf("连接错误/n"); 
return 3; 
} 
else 
{ 
//MessageBox(0,"连接成功","成功",MB_OK); 
printf("连接成功/n"); 
} 
ret=recv(smtp,szMessage,1024,0); 
/* sprintf(cmd,"HELO"); 
if (postcmd(smtp,cmd,szMessage,true)!=250) 
{ 
printf("HELO ERROR/n"); 
return 1; 
}*/ 
sprintf(cmd,"AUTH LOGIN"); 
if (postcmd(smtp,cmd,szMessage,true)!=334) 
{ 
printf("auth login error/n"); 
return 1; 
} 
base64enc(cmd,"cuilun"); //用户名base64编码 
//printf("%s",szMessage); 
postcmd(smtp,cmd,szMessage,true); 
base64enc(cmd,"password"); //密码 
if(postcmd(smtp,cmd,szMessage,true)!=235) 
{ 
printf("认证失败!/n"); 
return 1; 
} 
sprintf(cmd,"MAIL FROM:from@..."); //来自 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"RCPT TO: "); //收信 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"data"); 
postcmd(smtp,cmd,szMessage,true); 
sprintf(cmd,"from://");//////// 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"to:。。。");/////////////////// 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"subject:"); /////////////// 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"This is Only a TEST!"); 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"test"); 
postcmd(smtp,cmd,szMessage,false); 
sprintf(cmd,"%c%c.",13,10); 
if(postcmd(smtp,cmd,szMessage,true)==250) 
{ 
printf("发送成功!/n"); 
} 
else 
{ 
printf("发送失败!/n"); 
} 





//printf("/n%c/n",(('u'<<6)>>2)); 
//sprintf(cmd,"%c%c",13,10); 

closesocket(smtp); 
WSACleanup(); 
return 0; 
} 

int checkreturn(char *_msg) 
{ 
int i; 
int result=0; 
int t=1; 
for (i=2;i>=0;i--) 
{ 
result+=(_msg[i]-'0')*t; 
t=t*10; 
} 
return result; 
} 
int base64enc(char *_dest,char *_source) //编码，烦死了。 
{ 
int len=strlen((char*)_source); 
int i,j,k; 
int count=len/3; 
unsigned char *dest=(unsigned char*)_dest; 
unsigned char *source=(unsigned char*)_source; 
unsigned char temp[3]={0,0,0}; 
j=0; 
for(i=0;i<count;i++) 
{ 
dest[j]=source[i*3]/4; 
dest[j+1]=source[i*3]%4*16+source[i*3+1]/16; 
dest[j+2]=source[i*3+1]%16*4+source[i*3+2]/64; 
dest[j+3]=source[i*3+2]%64; 
j=j+4; 
} 
if(source[i*3]!=0) 
{ 
for (k=0;k<=2;k++) 
{ 
temp[k]=0; 
} 
for(k=0;k<=2;k++) 
{ 
if(source[i*3+k]!=0) temp[k]=source[i*3+k]; 
} 
dest[j]=temp[0]/4; 
dest[j+1]=temp[0]%4*16+temp[1]/16; 
if (temp[1]!=0) 
dest[j+2]=temp[1]%16*4+temp[2]/64; 
else 
dest[j+2]=127; 
if (temp[2]!=0) 
dest[j+3]=temp[2]%64; 
else 
dest[j+3]=127; 
j=j+4; 
} 
for(i=0;i<j;i++) 
{ 
if (dest[i]>=0&&dest[i]<=25) 
{ 
dest[i]+='A'; 
continue; 
} 
if (dest[i]>=26&&dest[i]<=51) 
{ 
dest[i]=dest[i]-26+'a'; 
continue; 
} 
if (dest[i]>=52&&dest[i]<=61) 
{ 
dest[i]=dest[i]-52+'0'; 
continue; 
} 
if (dest[i]==62) 
{ 
dest[i]='+'; 
continue; 
} 
if (dest[i]==63) 
{ 
dest[i]='/'; 
continue; 
} 
if(dest[i]==127) 
{ 
dest[i]='='; 
continue; 
} 
printf("/nencode error/n"); 
} 

dest[j]=0; 
return j; 
} 
int postcmd(SOCKET smtp,char * cmd,char *ret,bool rec) 
{ 
printf("发送:%s/n",cmd); 
int len=strlen(cmd); 
cmd[len]=13;cmd[len+1]=10;cmd[len+2]=0; 
send(smtp,cmd,strlen(cmd),0); 
if (rec){ 
recv(smtp,ret,1024,0); 
printf("接收:%s/n",ret); 
return checkreturn(ret); 
} 
return 0; 
}