#include <iostream>  #include <string>  #include <WinSock2.h> //適用平臺 Windows using namespace std; #pragma comment(lib, "ws2_32.lib") /*鏈接ws2_32.lib動態鏈接庫*/   int main() {  char buff[500]; //recv函數返回的結果  string message;   WSADATA wsaData;  WORD wVersionRequested = MAKEWORD(2, 1);  //WSAStarup，即WSA(Windows SocKNDs Asynchronous，Windows套接字異步)的啟動命令  int err = WSAStartup(wVersionRequested, &wsaData);  cout << "WSAStartup:" << err << endl;  SOCKET sockClient; //客戶端的套接字   sockClient = socket(AF_INET, SOCK_STREAM, 0); //建立socket對象    HOSTENT* pHostent;  pHostent = gethostbyname("smtp.126.com"); //得到有關于域名的信息  SOCKADDR_IN addrServer; //服務端地址  addrServer.sin_addr.S_un.S_addr = *((DWORD *)pHostent->h_addr_list[0]); //得到smtp服務器的網絡字節序的ip地址    addrServer.sin_family = AF_INET;  addrServer.sin_port = htons(25); //連接端口25   //int connect (SOCKET s , const struct sockaddr FAR *name , int namelen ); //函數原型  err = connect(sockClient, (SOCKADDR*)&addrServer, sizeof(SOCKADDR)); //向服務器發送請求   cout << "connect:" << err << endl;  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "connect:" << buff << endl;  /*  登錄郵件服務器  */  message = "ehlo 126.com/r/n";  send(sockClient, message.c_str(), message.length(), 0); //發送ehlo命令  buff[recv(sockClient, buff, 500, 0)] = '/0';   //接收返回值  cout << "helo:" << buff << endl;     //輸出返回值   message = "auth login /r/n";  send(sockClient, message.c_str(), message.length(), 0);  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "auth login:" << buff << endl;  /*  發送base64加密的用戶名、密碼  */  message = "xxxx/r/n"; //base64 編碼的用戶名  send(sockClient, message.c_str(), message.length(), 0);  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "usrname:" << buff << endl;   message = "xxxx/r/n";//base64 編碼的密碼  send(sockClient, message.c_str(), message.length(), 0);  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "password:" << buff << endl;  /*  使用 MAIL 命令指定發送者  使用 RCPT 命令指定接收者，可以重復使用RCPT指定多個接收者  */  message = "MAIL FROM:<xxxx@126.com> /r/nRCPT TO:<xxxx@126.com> /r/n";  send(sockClient, message.c_str(), message.length(), 0);   buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "mail from: " << buff << endl;  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "rcpt to: " << buff << endl;  /*  使用 DATA 命令告訴服務器要發送郵件內容  */  message = "DATA/r/n";  send(sockClient, message.c_str(), message.length(), 0);  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "data: " << buff << endl;  message = "From: Bob@example.com/r/n/ To: Alice@example.com/r/n/ Cc: theboss@example.com/r/n/ subject: subject/r/n/r/n/ Hello Alice/r/n/ This is a test message with 4 header fields and 4 lines in the message body/r/n/ your friend/r/n/ Bob/r/n./r/n"; //注意subject關鍵字與正文之間要有一個空行  send(sockClient, message.c_str(), message.length(), 0);  message = "QUIT/r/n";  send(sockClient, message.c_str(), message.length(), 0);  buff[recv(sockClient, buff, 500, 0)] = '/0';  cout << "QUIT:" << buff << endl;  system("pause"); }