C语言实现邮件发送功能(SMTP)源码

【实例截图】

【核心代码】

#include <stdio.h>
#include <string.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")
/**
*连接服务器
*/
SOCKET connect_server(char *host, int port);
void disconnect(SOCKET c);
void send_msg(SOCKET c, char *msg);
void recv_msg(SOCKET c);
char* base64_encode(const char* data, int data_len);

const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789 /=";



SOCKET connect_server(char *host, int port)
{
	WSADATA         wd;
	int ret = 0;
	SOCKET c;
	SOCKADDR_IN saddr;
	struct hostent *pHostent;

	ret = WSAStartup(MAKEWORD(2, 2), &wd);

	if (ret != 0)
	{
		return 0;
	}

	if (HIBYTE(wd.wVersion) != 2 || LOBYTE(wd.wVersion) != 2)
	{
		printf("Failed to initialize");
		WSACleanup();
		return 1;
	}



	c = socket(AF_INET, SOCK_STREAM, 0);

	pHostent = gethostbyname(host);
	//        printf("%s", inet_ntoa(*((struct in_addr*)pHostent->h_addr_list[0])));

	saddr.sin_addr.S_un.S_addr = *((unsigned long*)pHostent->h_addr_list[0]);
	saddr.sin_family = AF_INET;
	saddr.sin_port = htons(port);

	connect(c, (SOCKADDR*)&saddr, sizeof(SOCKADDR));

	return c;

}

void disconnect(SOCKET c)
{
	closesocket(c);
	WSACleanup();
}

void recv_msg(SOCKET c)
{
	char text[BUFSIZ];
	strnset(text, '\0', BUFSIZ);
	recv(c, text, BUFSIZ, 0);
	printf("\nrecv:%s\n", text);
}

void send_msg(SOCKET c, char *msg)
{
	printf("\nsend:%s\n", msg);
	send(c, msg, strlen(msg), 0);
}

char *base64_encode(const char* data, int data_len)
{
	//int data_len = strlen(data); 
	int prepare = 0;
	int ret_len;
	int temp = 0;
	char *ret = NULL;
	char *f = NULL;
	int tmp = 0;
	char changed[4];
	int i = 0;
	ret_len = data_len / 3;
	temp = data_len % 3;
	if (temp > 0)
	{
		ret_len  = 1;
	}
	ret_len = ret_len * 4   1;
	ret = (char *)malloc(ret_len);

	if (ret == NULL)
	{
		printf("No enough memory.\n");
		exit(0);
	}
	memset(ret, 0, ret_len);
	f = ret;
	while (tmp < data_len)
	{
		temp = 0;
		prepare = 0;
		memset(changed, '\0', 4);
		while (temp < 3)
		{
			//printf("tmp = %d\n", tmp); 
			if (tmp >= data_len)
			{
				break;
			}
			prepare = ((prepare << 8) | (data[tmp] & 0xFF));
			tmp  ;
			temp  ;
		}
		prepare = (prepare << ((3 - temp) * 8));
		//printf("before for : temp = %d, prepare = %d\n", temp, prepare); 
		for (i = 0; i < 4; i  )
		{
			if (temp < i)
			{
				changed[i] = 0x40;
			}
			else
			{
				changed[i] = (prepare >> ((3 - i) * 6)) & 0x3F;
			}
			*f = base[changed[i]];
			//printf("%.2X", changed[i]); 
			f  ;
		}
	}
	*f = '\0';

	return ret;

}

int main(void)
{
	char sendbuf[BUFSIZ], recvbuf[BUFSIZ], recv_email[BUFSIZ], subject[BUFSIZ], content[BUFSIZ], email[200], pass[200];
	char *pstr = NULL;
	char *host = "smtp.163.com";
	int port = 25;
	SOCKET c;

	c = connect_server(host, port);

	//接受服务器发来的数据
	recv_msg(c);

	//跟服务器打招呼
	send_msg(c, "helo qq\r\n");

	//接受服务器发来的数据
	recv_msg(c);

	//告诉服务器要登陆
	send_msg(c, "auth login\r\n");

	//接受服务器发来的数据
	recv_msg(c);

	//提示用户输入邮箱地址
	printf("=====login email====\nemail ID:");
	scanf("%s", email);
	printf("password:");
	scanf("%s", pass);

	/*************发送邮箱地址和密码**************/

	//加密邮箱地址
	pstr = base64_encode(email, strlen(email));

	//拼接邮箱地址, 用strcpy是为了省去清空sendbuf
	strcpy(sendbuf, pstr);

	//加回车换行        
	strcat(sendbuf, "\r\n\0");
	send_msg(c, sendbuf);

	//接收返回内容并显示
	recv_msg(c);

	//释放内存,在base64加密函数里面分配的
	free(pstr);



	//加密邮箱密码
	pstr = base64_encode(pass, strlen(pass));
	strcpy(sendbuf, pstr);
	strcat(sendbuf, "\r\n\0");
	send_msg(c, sendbuf);
	recv_msg(c);
	free(pstr);

	/**************填写收件人,发件人信息***********************/


	//告诉服务器发件人是谁
	strcpy(sendbuf, "mail from:<");
	strcat(sendbuf, email);
	strcat(sendbuf, ">");
	strcat(sendbuf, "\r\n\0");
	send_msg(c, sendbuf);
	recv_msg(c);


	//告诉服务器收件人是谁
	printf("Please enter the recipient mailbox:");
	scanf("%s", recv_email);

	strcpy(sendbuf, "rcpt to:<");
	strcat(sendbuf, recv_email);
	strcat(sendbuf, ">");
	strcat(sendbuf, "\r\n\0");
	send_msg(c, sendbuf);
	recv_msg(c);



	/******************发送邮件内容*********************************/

	send_msg(c, "data\r\n");
	recv_msg(c);

	printf("please enter the title:");
	scanf("%s", subject);
	printf("please enter the content:");
	scanf("%s", content);




	//这里填写发件人，可以随便填写，可用于伪造邮件
	strcpy(sendbuf, "From: ");
	strcat(sendbuf, email);
	strcat(sendbuf, "\n");

	strcat(sendbuf, "To: ");
	strcat(sendbuf, recv_email);
	strcat(sendbuf, "\n");

	//发送标题和内容
	strcat(sendbuf, "subject:");
	strcat(sendbuf, subject);
	strcat(sendbuf, "\r\n\r\n");
	strcat(sendbuf, content);
	strcat(sendbuf, "\r\n.\r\n\0");
	send_msg(c, sendbuf);
	recv_msg(c);

	disconnect(c);

	printf("mail is already send to:%s\n", recv_email);

	return 0;
}