电子邮件发送的原理以及简易实现

在代码開始之前，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easy懂多了！

以下以163邮箱为例！



先键入telnet命令。然后连接到网易的smtpserver,使用25号port.



接着看下图:

<<<<<<


从如今開始。我们能够模拟发送信件的过程了!

发送命令：EHLO hello (hello能够随意替换)



然后我们请求登陆！

发送命令: AUTH LOGIN



然后发送自己账户的username的base64编码(不要@XXX.com)过去!我用的一个測试邮箱it_is_just_a_test@163.com,it_is_just_a_test的base64编码是aXRfaXNfanVzdF9hX3Rlc3Q=



然后将自己的password的base64编码发过去！我的password的base64编码是MTk5MzA3MTRseWg=



server告诉你认证成功了！我们如今就能够发送邮件了!

先发送邮件说明:MAIL FROM: <it_is_just_a_test@163.com>

然后发送目的邮箱说明:RCPT TO: <it_is_just_a_test@126.com>

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: it_is_just_a_test@163.com

To: it_is_just_a_test@126.com

Subject: 測试一下

MIME-Version: 1.0

这是一封測试邮件!!! .

(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



当信件发送完毕了之后。我们能够利用quit命令关闭与server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] = "it_is_just_a_test@163.com"; //自己的邮箱名称
char password[256] = "19930714lyh"; //自己邮箱的密码
char targetEmail[256] = "it_is_just_a_test@126.com"; //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] = "这是一封測试邮件！

非常高兴我的第一个邮件client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smtpserver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server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,		//client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) //不过接收数据
{
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", "it_is_just_a_test@163.com");
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还有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username,如从"13203200199@163.com"得到"13203200199"
char base[256];
StringToBase64(pUerName, base); //得到username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username，并接收server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server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();
}