电子邮件发送的原理以及简易实现
在代码开始之前，我们先手工模拟一遍发送电子邮件的过程，那么接下来的代码你就容易懂多了！
下面以163邮箱为例！
先键入telnet命令，然后连接到网易的smtp服务器,使用25号端口.
接着看下图:
<<<<<<
从现在开始，我们可以模拟发送信件的过程了!
发送命令：EHLO hello (hello可以任意替换)
然后我们请求登陆！
发送命令: AUTH LOGIN
然后发送自己账户的用户名的base64编码(不要@XXX.com)过去!我用的一个测试邮箱[email protected],it_is_just_a_test的base64编码是aXRfaXNfanVzdF9hX3Rlc3Q=
然后将自己的密码的base64编码发过去！我的密码的base64编码是MTk5MzA3MTRseWg=
服务器告诉你认证成功了！我们现在就可以发送邮件了!
先发送邮件说明:MAIL FROM: <[email protected]>
然后发送目的邮箱说明:RCPT TO: <[email protected]>
然后请求发送邮件:DATA
然后发送邮件头和邮件体，发送数据：
From: [email protected]
Subject: 测试一下
MIME-Version: 1.0
这是一封测试邮件!!! .
(在正文输入结束时回车输入一个 . （英文输入法下的句号）然后再回车，表示正文部分的结束。这时将显示邮件成功发送的信息。)<CR><LF>表示的是回车
当信件发送完成了之后，我们可以利用quit命令关闭与服务器的连接！
基本原理就是这样了：然后我们来看代码吧！(利用程序发送的时候无非就是把回车换成"\r\n"!)
#include <iostream> #include <WinSock2.h> #include <windows.h> #include <string.h> using namespace std; #pragma comment(lib, "ws2_32.lib") /*链接ws2_32.lib动态链接库*/ const int MAXSIZE = 1024; int srvPort = 25; char srvDomain[256] = "smtp.163.com"; char userName[256] = "[email protected]"; //自己的邮箱名称 char password[256] = "19930714lyh"; //自己邮箱的密码 char targetEmail[256] = "[email protected]"; //要发送的邮件地址 char emailTitle[256] = "你好！我是李树花开！"; //邮件主题 char content[256] = "这是一封测试邮件！很高兴我的第一个邮件客户端制作成功了！";//邮件正文 SOCKET CreateConn(char* pWebsite,int port) { //为建立socket对象做准备，初始化环境 SOCKET sockClient = socket(AF_INET,SOCK_STREAM,0); //建立socket对象 SOCKADDR_IN addrSrv; HOSTENT* pHostent; pHostent = gethostbyname(pWebsite); //得到有关于域名的信息 addrSrv.sin_addr.S_un.S_addr = *((DWORD *)pHostent->h_addr_list[0]); //得到smtp服务器的网络字节序的ip地址 addrSrv.sin_family=AF_INET; addrSrv.sin_port=htons(port); int tf = connect(sockClient,(SOCKADDR*)&addrSrv,sizeof(SOCKADDR)); //向服务器发送请求 if(tf!=0) { return 0; //printf("链接失败\n"); } return sockClient; } //int DoWhat是否接受数据 void SendAndRecvMsg( SOCKET sockClient, //客户端的套接字 char* pMessage, //要发送的消息 int Messagelen, //消息的长度 int DoWhat, //造作的类型 char* recvBuf, //接收的缓冲区 int recvBufLen //缓冲区长度 ) { char lpMessage[256] = {0}; memcpy(lpMessage, pMessage, Messagelen); printf("\n\n%s \n", lpMessage); if (DoWhat == 0) { send(sockClient, lpMessage, Messagelen, 0); memset(recvBuf , 0, recvBufLen); DWORD num = recv(sockClient, recvBuf, recvBufLen, 0); //接收数据 printf("%s \n", recvBuf); int i = 0; while(i != num) { printf("%02X ", recvBuf[i++]); if((i)%16 == 0) { printf("\n"); } } printf("\n"); } else if (DoWhat == 1) { send(sockClient, lpMessage, Messagelen, 0); } else if (DoWhat == 2) //仅仅是接收数据 { memset(recvBuf, 0, recvBufLen); DWORD num=recv(sockClient,recvBuf,recvBufLen,0); //接收数据 cout << recvBuf << endl; int i = 0; while(i < num) { printf("%02X ", (byte)recvBuf[i++]); if((i)%16 == 0) { printf("\n"); } } printf("\n"); } } int GetStrLen(char* pString) //得到字符串的长度 { int i = 0; while(pString[i++] != 0); return i-1; } void StringToBase64(const char *src,char *dst) {/*将字符串变为base64编码*/ int i = 0; char *p = dst; int d= strlen(src) - 3; static const char Base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; //for(i=0;i<strlen(src)-3;i+=3) ;if (strlen(src)-3)<0 there is a buf for(i=0;i<=d;i+=3) { *p++ = Base64[((*(src + i)) >> 2) & 0x3f]; *p++ = Base64[(((*(src + i)) & 0x3) << 4) + ((*(src + i + 1)) >> 4)]; *p++ = Base64[((*(src + i + 1) & 0xf) << 2) + ((*(src + i + 2)) >> 6)]; *p++ = Base64[(*(src + i + 2)) & 0x3f]; } if((strlen(src) - i) == 1) { *p++ = Base64[((*(src + i)) >> 2) & 0x3f]; *p++ = Base64[((*(src + i)) & 0x3) << 4]; *p++ = '='; *p++ = '='; } if((strlen(src) - i) == 2) { *p++ = Base64[((*(src + i)) >> 2) & 0x3f]; *p++ = Base64[(((*(src + i)) & 0x3) << 4) + ((*(src + i + 1)) >> 4)]; *p++ = Base64[((*(src + i + 1) & 0xf) << 2)]; *p++ = '='; } *p = '\0'; } bool FormatEmail(char* pFrom, char* pTo, char* pSubject, char* pMessage, char* Email) {/*格式化要发送的内容*/ lstrcat(Email, "From: "); lstrcat(Email, pFrom); lstrcat(Email, "\r\n"); lstrcat(Email, "To: "); lstrcat(Email, pTo); lstrcat(Email, "\r\n"); lstrcat(Email, "Subject: "); lstrcat(Email, pSubject); lstrcat(Email, "\r\n"); lstrcat(Email, "MIME-Version: 1.0"); lstrcat(Email, "\r\n"); lstrcat(Email, "\r\n"); lstrcat(Email, pMessage); lstrcat(Email, "\r\n.\r\n"); return TRUE; } void main() { WORD wVersionRequested; WSADATA wsaData; int err; wVersionRequested = MAKEWORD(2, 1); err = WSAStartup(wVersionRequested, &wsaData); SOCKET sockClient = CreateConn(srvDomain, srvPort); //网易smtp邮箱，25号端口 char buff[MAXSIZE]; memset(buff, 0, sizeof(char) * MAXSIZE); //清零 SendAndRecvMsg(sockClient, 0, 0, 2, buff, MAXSIZE); //接收数据 char UserNameToSendEmail[256] = {0}; sprintf(UserNameToSendEmail, "EHLO %s", "[email protected]"); lstrcat(UserNameToSendEmail, "\r\n\0"); SendAndRecvMsg(sockClient, UserNameToSendEmail, GetStrLen(UserNameToSendEmail), 0, buff, MAXSIZE); //既接收也发送 SendAndRecvMsg(sockClient, "AUTH LOGIN\r\n", strlen("AUTH LOGIN\r\n"), 0, buff, MAXSIZE); //请求登陆 char pUerName[256] = {0}; //strstr函数搜索一个字符串在另一个字符串中的第一次出现，并返回第一次出现位置的指针 DWORD p = strstr(userName,"@") - userName; memcpy(pUerName, userName, p); //得到用户名,如从"[email protected]"得到"13203200199" char base[256]; StringToBase64(pUerName, base); //得到用户名的base64编码 char str[MAXSIZE]; memset(str, 0, MAXSIZE); sprintf(str, "%s\r\n", base/*"MTMyMDMyMDAxOTk="*/); SendAndRecvMsg(sockClient, str, lstrlen(str), 0, buff, MAXSIZE); //发送用户名，并接收服务器的返回 StringToBase64(password, base); memset(str, 0, 1024); sprintf(str, "%s\r\n", base); SendAndRecvMsg(sockClient, str, lstrlen(str),0, buff, MAXSIZE); //发送用户密码，并接收服务器的返回 char MailFrom[256] = {0}; sprintf(MailFrom, "MAIL FROM: <%s>\r\n", userName); SendAndRecvMsg(sockClient, MailFrom, lstrlen(MailFrom), 0, buff, MAXSIZE); char RcptTo[256] = {0}; sprintf(RcptTo, "RCPT TO: <%s>\r\n", targetEmail); SendAndRecvMsg(sockClient, RcptTo, lstrlen(RcptTo), 0, buff, MAXSIZE); SendAndRecvMsg(sockClient, "DATA\r\n", lstrlen("DATA\r\n"), 0, buff, MAXSIZE); char Email[1024] = {0}; FormatEmail(userName, targetEmail, emailTitle, content, Email); SendAndRecvMsg(sockClient,Email,lstrlen(Email), 0, buff, MAXSIZE); SendAndRecvMsg(sockClient,"QUIT\r\n", lstrlen("QUIT\r\n"), 0, buff, MAXSIZE); closesocket(sockClient); WSACleanup(); }