Linux C实现发邮件功能

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/fcntl.h>
#include <sys/stat.h>
 
#define SOCKET_ERROR -1
#define IPSTR "220.181.12.12"
#define PRINT(x) printf("%s
",(x))
 
int sockfd;
int ret;
char *send_data;
char *recv_data;
char From[128];
char To[128];
char Date[128];
char Subject[512];
char Context[6000]={0};
char buffer[1024];

int connectHost(const char *smtpaddr)
{
    struct sockaddr_in servaddr;
    sockfd = socket(AF_INET,SOCK_STREAM,0);
    if(sockfd < 0)
    {
        printf("Create socket error!
");
        return -1;
    }
    bzero(&servaddr,sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(25);
    
    if(inet_pton(AF_INET, IPSTR, &servaddr.sin_addr) <= 0 ) 
    {
        printf("inet_pton error!
");
        return -1;
    };

    if (connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr)) < 0)    
    {
        printf("Connect failed... 
");
        return -1;
    }
    printf("Connect to %s.... 
", IPSTR);
     
    memset(buffer, 0, sizeof(buffer));
     
    if(recv(sockfd, buffer, sizeof(buffer), 0) < 0)
    {    
        printf("receive failed... 
");
        return -1;
    }
    else 
    {        
         printf("%s
", buffer);
    }
    return sockfd;    
}
 

int getResponse()
{    
    memset(buffer,0,sizeof(buffer));
    ret = recv(sockfd,buffer,1024,0);
    if(ret == SOCKET_ERROR)
    {
        printf("receive nothing
");
        return -1;
    }
    buffer[ret]='