這段程式碼我花了整整一天來編寫，如果轉載，請註明出處，謝謝！

   前面的一篇文章已經講了如何傳送郵件正文，原理我就不再敘述了，要了解的同學請到這裡檢視!

   網上很多傳送郵件附件的程式碼都不能用，所以我用心寫了一個，直接封裝成了一個類，需要的同學可以直接呼叫這個類來發送郵件,純c++程式碼。(在VS2013下測試完美通過!)

   廢話不多說，直接上程式碼!

   Smtp.h

#ifndef __SMTP_H__ //避免重複包含
#define __SMTP_H__

#include <iostream>
#include <list>
#include <WinSock2.h>
using namespace std;

const int MAXLEN = 1024;
const int MAX_FILE_LEN = 6000;

static const char base64Char[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

struct FILEINFO /*用來記錄檔案的一些資訊*/
{
	char fileName[128]; /*檔名稱*/
	char filePath[256]; /*檔案絕對路徑*/
};

class CSmtp
{
public:
	CSmtp(void);
	CSmtp(
		int port,
		string srvDomain,	//smtp伺服器域名
		string userName,	//使用者名稱
		string password,	//密碼
		string targetEmail, //目的郵件地址
		string emailTitle,  //主題
		string content       //內容
		);
public:
	~CSmtp(void);
public:
	int port;
public:
	string domain;
	string user;
	string pass;
	string targetAddr;
	string title;
	string content;
	/*為了方便新增檔案，刪除檔案神馬的，使用list容器最為方便，相信大家在資料結構裡面都學過*/
	list <FILEINFO *> listFile;

public:
	char buff[MAXLEN + 1];
	int buffLen;
	SOCKET sockClient;	//客戶端的套接字
public:
	bool CreateConn(); /*建立連線*/

	bool Send(string &message);
	bool Recv();

	void FormatEmailHead(string &email);//格式化要傳送的郵件頭部
	int Login();
	bool SendEmailHead();		//傳送郵件頭部資訊
	bool SendTextBody();	    //傳送文字資訊
	//bool SendAttachment();	    //傳送附件
	int SendAttachment_Ex();
	bool SendEnd();
public:
	void AddAttachment(string &filePath); //新增附件
	void DeleteAttachment(string &filePath); //刪除附件
	void DeleteAllAttachment(); //刪除所有的附件

	void SetSrvDomain(string &domain);
	void SetUserName(string &user);
	void SetPass(string &pass);
	void SetTargetEmail(string &targetAddr);
	void SetEmailTitle(string &title);
	void SetContent(string &content);
	void SetPort(int port);
	int SendEmail_Ex();
	/*關於錯誤碼的說明:1.網路錯誤導致的錯誤2.使用者名稱錯誤3.密碼錯誤4.檔案不存在0.成功*/
	char* base64Encode(char const* origSigned, unsigned origLength);
};

#endif // !__SMTP_H__
 

#include "Smtp.h"
#include <iostream>
#include <fstream>
using namespace std;

#pragma  comment(lib, "ws2_32.lib")	/*連結ws2_32.lib動態連結庫*/

/*base64採用別人的編碼,不過，這不是重點，重點是我完成了我的一個比較好的郵件傳送客戶端*/
char* CSmtp::base64Encode(char const* origSigned, unsigned origLength)
{
	unsigned char const* orig = (unsigned char const*)origSigned; // in case any input bytes have the MSB set
	if (orig == NULL) return NULL;

	unsigned const numOrig24BitValues = origLength / 3;
	bool havePadding = origLength > numOrig24BitValues * 3;
	bool havePadding2 = origLength == numOrig24BitValues * 3 + 2;
	unsigned const numResultBytes = 4 * (numOrig24BitValues + havePadding);
	char* result = new char[numResultBytes + 3]; // allow for trailing '/0'

	// Map each full group of 3 input bytes into 4 output base-64 characters:
	unsigned i;
	for (i = 0; i < numOrig24BitValues; ++i)
	{
		result[4 * i + 0] = base64Char[(orig[3 * i] >> 2) & 0x3F];
		result[4 * i + 1] = base64Char[(((orig[3 * i] & 0x3) << 4) | (orig[3 * i + 1] >> 4)) & 0x3F];
		result[4 * i + 2] = base64Char[((orig[3 * i + 1] << 2) | (orig[3 * i + 2] >> 6)) & 0x3F];
		result[4 * i + 3] = base64Char[orig[3 * i + 2] & 0x3F];
	}

	// Now, take padding into account.  (Note: i == numOrig24BitValues)
	if (havePadding)
	{
		result[4 * i + 0] = base64Char[(orig[3 * i] >> 2) & 0x3F];
		if (havePadding2)
		{
			result[4 * i + 1] = base64Char[(((orig[3 * i] & 0x3) << 4) | (orig[3 * i + 1] >> 4)) & 0x3F];
			result[4 * i + 2] = base64Char[(orig[3 * i + 1] << 2) & 0x3F];
		}
		else
		{
			result[4 * i + 1] = base64Char[((orig[3 * i] & 0x3) << 4) & 0x3F];
			result[4 * i + 2] = '=';
		}
		result[4 * i + 3] = '=';
	}

	result[numResultBytes] = '\0';
	return result;
}
CSmtp::CSmtp(void)
{
	this->content = "";
	this->port = 25;
	this->user = "";
	this->pass = "";
	this->targetAddr = "";
	this->title = "";
	this->domain = "";

	WORD wVersionRequested;
	WSADATA wsaData;
	int err;
	wVersionRequested = MAKEWORD(2, 1);
	err = WSAStartup(wVersionRequested, &wsaData);
	this->sockClient = 0;

}

CSmtp::~CSmtp(void)
{
	DeleteAllAttachment();
	closesocket(sockClient);
	WSACleanup();
}


CSmtp::CSmtp(
	int port,
	string srvDomain,
	string userName,
	string password,
	string targetEmail,
	string emailTitle,
	string content
	)
{
	this->content = content;
	this->port = port;
	this->user = userName;
	this->pass = password;
	this->targetAddr = targetEmail;
	this->title = emailTitle;
	this->domain = srvDomain;

	WORD wVersionRequested;
	WSADATA wsaData;
	int err;
	wVersionRequested = MAKEWORD(2, 1);
	err = WSAStartup(wVersionRequested, &wsaData);
	this->sockClient = 0;
}

bool CSmtp::CreateConn()
{
	//為建立socket物件做準備，初始化環境
	SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0); //建立socket物件
	SOCKADDR_IN addrSrv;
	HOSTENT* pHostent;
	pHostent = gethostbyname(domain.c_str());  //得到有關於域名的資訊

	addrSrv.sin_addr.S_un.S_addr = *((DWORD *)pHostent->h_addr_list[0]);	//得到smtp伺服器的網路位元組序的ip地址   
	addrSrv.sin_family = AF_INET;
	addrSrv.sin_port = htons(port);
	int err = connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR));   //向伺服器傳送請求 
	if (err != 0)
	{
		return false;
		//printf("連結失敗\n");
	}
	this->sockClient = sockClient;
	if (false == Recv())
	{
		return false;
	}
	return true;
}

bool CSmtp::Send(string &message)
{
	int err = send(sockClient, message.c_str(), message.length(), 0);
	if (err == SOCKET_ERROR)
	{
		return false;
	}
	string message01;
	cout << message.c_str() << endl;
	return true;
}

bool CSmtp::Recv()
{
	memset(buff, 0, sizeof(char)* (MAXLEN + 1));
	int err = recv(sockClient, buff, MAXLEN, 0); //接收資料
	if (err == SOCKET_ERROR)
	{
		return false;
	}
	buff[err] = '\0';
	cout << buff << endl;
	return true;
}

int CSmtp::Login()
{
	string sendBuff;
	sendBuff = "EHLO ";
	sendBuff += user;
	sendBuff += "\r\n";

	if (false == Send(sendBuff) || false == Recv()) //既接收也傳送
	{
		return 1; /*1表示傳送失敗由於網路錯誤*/
	}

	sendBuff.empty();
	sendBuff = "AUTH LOGIN\r\n";
	if (false == Send(sendBuff) || false == Recv()) //請求登陸
	{
		return 1; /*1表示傳送失敗由於網路錯誤*/
	}

	sendBuff.empty();
	int pos = user.find('@', 0);
	sendBuff = user.substr(0, pos); //得到使用者名稱

	char *ecode;
	/*在這裡順帶扯一句，關於string類的length函式與C語言中的strlen函式的區別,strlen計算出來的長度，只到'\0'字元為止,而string::length()函式實際上返回的是string類中字元陣列的大小,你自己可以測試一下，這也是為什麼我下面不使用string::length()的原因*/

	ecode = base64Encode(sendBuff.c_str(), strlen(sendBuff.c_str()));
	sendBuff.empty();
	sendBuff = ecode;
	sendBuff += "\r\n";
	delete[]ecode;

	if (false == Send(sendBuff) || false == Recv()) //傳送使用者名稱，並接收伺服器的返回
	{
		return 1; /*錯誤碼1表示傳送失敗由於網路錯誤*/
	}

	sendBuff.empty();
	ecode = base64Encode(pass.c_str(), strlen(pass.c_str()));
	sendBuff = ecode;
	sendBuff += "\r\n";
	delete[]ecode;

	if (false == Send(sendBuff) || false == Recv()) //傳送使用者密碼，並接收伺服器的返回
	{
		return 1; /*錯誤碼1表示傳送失敗由於網路錯誤*/
	}

	if (NULL != strstr(buff, "550"))
	{
		return 2;/*錯誤碼2表示使用者名稱錯誤*/
	}

	if (NULL != strstr(buff, "535")) /*535是認證失敗的返回*/
	{
		return 3; /*錯誤碼3表示密碼錯誤*/
	}
	return 0;
}

bool CSmtp::SendEmailHead()		//傳送郵件頭部資訊
{
	string sendBuff;
	sendBuff = "MAIL FROM: <" + user + ">\r\n";
	if (false == Send(sendBuff) || false == Recv())
	{
		return false; /*表示傳送失敗由於網路錯誤*/
	}


	sendBuff.empty();
	sendBuff = "RCPT TO: <" + targetAddr + ">\r\n";
	if (false == Send(sendBuff) || false == Recv())
	{
		return false; /*表示傳送失敗由於網路錯誤*/
	}

	sendBuff.empty();
	sendBuff = "DATA\r\n";
	if (false == Send(sendBuff) || false == Recv())
	{
		return false; //表示傳送失敗由於網路錯誤
	}

	sendBuff.empty();
	FormatEmailHead(sendBuff);
	if (false == Send(sendBuff))
		//傳送完頭部之後不必呼叫接收函式,因為你沒有\r\n.\r\n結尾，伺服器認為你沒有發完資料，所以不會返回什麼值
	{
		return false; /*表示傳送失敗由於網路錯誤*/
	}
	return true;
}

void CSmtp::FormatEmailHead(string &email)
{/*格式化要傳送的內容*/
	email = "From: ";
	email += user;
	email += "\r\n";

	email += "To: ";
	email += targetAddr;
	email += "\r\n";

	email += "Subject: ";
	email += title;
	email += "\r\n";

	email += "MIME-Version: 1.0";
	email += "\r\n";

	email += "Content-Type: multipart/mixed;boundary=qwertyuiop";
	email += "\r\n";
	email += "\r\n";
}

bool CSmtp::SendTextBody()  /*傳送郵件文字*/
{
	string sendBuff;
	sendBuff = "--qwertyuiop\r\n";
	sendBuff += "Content-Type: text/plain;";
	sendBuff += "charset=\"gb2312\"\r\n\r\n";
	sendBuff += content;
	sendBuff += "\r\n\r\n";
	return Send(sendBuff);
}

int CSmtp::SendAttachment_Ex() /*傳送附件*/
{
	for (list<FILEINFO *>::iterator pIter = listFile.begin(); pIter != listFile.end(); pIter++)
	{
		cout << "Attachment is sending ~~~~~" << endl;
		cout << "Please be patient!" << endl;
		string sendBuff;
		sendBuff = "--qwertyuiop\r\n";
		sendBuff += "Content-Type: application/octet-stream;\r\n";
		sendBuff += " name=\"";
		sendBuff += (*pIter)->fileName;
		sendBuff += "\"";
		sendBuff += "\r\n";

		sendBuff += "Content-Transfer-Encoding: base64\r\n";
		sendBuff += "Content-Disposition: attachment;\r\n";
		sendBuff += " filename=\"";
		sendBuff += (*pIter)->fileName;
		sendBuff += "\"";

		sendBuff += "\r\n";
		sendBuff += "\r\n";
		Send(sendBuff);
		ifstream ifs((*pIter)->filePath, ios::in | ios::binary);
		if (false == ifs.is_open())
		{
			return 4; /*錯誤碼4表示檔案開啟錯誤*/
		}
		char fileBuff[MAX_FILE_LEN];
		char *chSendBuff;
		memset(fileBuff, 0, sizeof(fileBuff));
		/*檔案使用base64加密傳送*/
		while (ifs.read(fileBuff, MAX_FILE_LEN))
		{
			//cout << ifs.gcount() << endl;
			chSendBuff = base64Encode(fileBuff, MAX_FILE_LEN);
			chSendBuff[strlen(chSendBuff)] = '\r';
			chSendBuff[strlen(chSendBuff)] = '\n';
			send(sockClient, chSendBuff, strlen(chSendBuff), 0);
			delete[]chSendBuff;
		}
		//cout << ifs.gcount() << endl;
		chSendBuff = base64Encode(fileBuff, ifs.gcount());
		chSendBuff[strlen(chSendBuff)] = '\r';
		chSendBuff[strlen(chSendBuff)] = '\n';
		int err = send(sockClient, chSendBuff, strlen(chSendBuff), 0);

		if (err != strlen(chSendBuff))
		{
			cout << "檔案傳送出錯!" << endl;
			return 1;
		}
		delete[]chSendBuff;
	}
	return 0;
}

bool CSmtp::SendEnd() /*傳送結尾資訊*/
{
	string sendBuff;
	sendBuff = "--qwertyuiop--";
	sendBuff += "\r\n.\r\n";
	if (false == Send(sendBuff) || false == Recv())
	{
		return false;
	}
	cout << buff << endl;
	sendBuff.empty();
	sendBuff = "QUIT\r\n";
	return (Send(sendBuff) && Recv());
}

int CSmtp::SendEmail_Ex()
{
	if (false == CreateConn())
	{
		return 1;
	}
	//Recv();
	int err = Login(); //先登入
	if (err != 0)
	{
		return err; //錯誤程式碼必須要返回
	}
	if (false == SendEmailHead()) //傳送EMAIL頭部資訊
	{
		return 1; /*錯誤碼1是由於網路的錯誤*/
	}
	if (false == SendTextBody())
	{
		return 1; /*錯誤碼1是由於網路的錯誤*/
	}
	err = SendAttachment_Ex();
	if (err != 0)
	{
		return err;
	}
	if (false == SendEnd())
	{
		return 1; /*錯誤碼1是由於網路的錯誤*/
	}
	return 0; /*0表示沒有出錯*/
}

void CSmtp::AddAttachment(string &filePath) //新增附件
{
	FILEINFO *pFile = new FILEINFO;
	strcpy_s(pFile->filePath, filePath.c_str());
	const char *p = filePath.c_str();
	strcpy_s(pFile->fileName, p + filePath.find_last_of("\\") + 1);
	listFile.push_back(pFile);
}

void CSmtp::DeleteAttachment(string &filePath) //刪除附件
{
	list<FILEINFO *>::iterator pIter;
	for (pIter = listFile.begin(); pIter != listFile.end(); pIter++)
	{
		if (strcmp((*pIter)->filePath, filePath.c_str()) == 0)
		{
			FILEINFO *p = *pIter;
			listFile.remove(*pIter);
			delete p;
			break;
		}
	}
}

void CSmtp::DeleteAllAttachment() /*刪除所有的檔案*/
{
	for (list<FILEINFO *>::iterator pIter = listFile.begin(); pIter != listFile.end();)
	{
		FILEINFO *p = *pIter;
		pIter = listFile.erase(pIter);
		delete p;
	}
}

void CSmtp::SetSrvDomain(string &domain)
{
	this->domain = domain;
}

void CSmtp::SetUserName(string &user)
{
	this->user = user;
}

void CSmtp::SetPass(string &pass)
{
	this->pass = pass;
}
void CSmtp::SetTargetEmail(string &targetAddr)
{
	this->targetAddr = targetAddr;
}
void CSmtp::SetEmailTitle(string &title)
{
	this->title = title;
}
void CSmtp::SetContent(string &content)
{
	this->content = content;
}
void CSmtp::SetPort(int port)
{
	this->port = port;
}
 

   main.cpp

#include "Smtp.h"
#include <iostream>
using namespace std;

int main()
{

	CSmtp smtp(
		25,								/*smtp埠*/
		"smtp.163.com",					/*smtp伺服器地址*/
		"[email protected]",	/*你的郵箱地址*/
		"XXXXXXX",					/*郵箱密碼*/
		"[email protected]",	/*目的郵箱地址*/
		"好啊!",							/*主題*/
		"XXX同學，你好！收到請回復！"		/*郵件正文*/
		);
	/**
	//新增附件時注意,\一定要寫成\\，因為轉義字元的緣故
	string filePath("D:\\課程設計報告.doc");
	smtp.AddAttachment(filePath);
	*/
	
	/*還可以呼叫CSmtp::DeleteAttachment函式刪除附件，還有一些函式，自己看標頭檔案吧!*/
	//filePath = "C:\\Users\\李懿虎\\Desktop\\sendEmail.cpp";
	//smtp.AddAttachment(filePath);

	int err;
	if ((err = smtp.SendEmail_Ex()) != 0)
	{
		if (err == 1)
			cout << "錯誤1: 由於網路不暢通，傳送失敗!" << endl;
		if (err == 2)
			cout << "錯誤2: 使用者名稱錯誤,請核對!" << endl;
		if (err == 3)
			cout << "錯誤3: 使用者密碼錯誤，請核對!" << endl;
		if (err == 4)
			cout << "錯誤4: 請檢查附件目錄是否正確，以及檔案是否存在!" << endl;
	}
	system("pause");
	return 0;
}
 

        在VS2005下面，很有可能會出現帶中文的目錄或者中文名檔案打不開的情況，這個時候這麼解決：在兩個建構函式裡面的第一句加上:setlocale(LC_ALL,"Chinese-simplified");這一句話即可解決！

     在VS2013裡面貌似這個程式可以執行，微軟這朵奇葩！不說了！

     請儘量不使用QQ郵箱登陸，因為我試過，貌似連不上。qq郵箱的伺服器返回告訴你要求安全的連線，用SSL什麼的，哎，qq也是朵奇葩！