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it_is_just_a_test@163.com,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: <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: 测试一下
MIME-Version: 1.0
这是一封测试邮件!!! .
(在正文输入结束时输入一个 . （英文输入法下的句号）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。)
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] = "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", "13203200199@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"13203200199@163.com"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();
}电子邮件发送的原理以及简易实现,布布扣,bubuko.com
原文地址：http://blog.csdn.net/lishuhuakai/article/details/27503503
