c 언어로 메일보내는 소스입니다.

BusyBox v1.13.4 (2014-10-23 04:01:34 PDT) multi-call binary
 
Usage: sendmail [OPTIONS] [rcpt]...
 
Send an email
 
Options:
        -w timeout      Network timeout
        -H [user:pass@]server[:port] Server
        -S              Use openssl connection helper for secure servers
        -N type         Request delivery notification. Type is ignored
        -f sender       Sender
        -F fullname     Sender full name. Overrides $NAME
        -s subject      Subject
        -j charset      Assume charset for body and subject (us-ascii)
        -a file         File to attach. May be multiple
        -H "prog args..." Use external connection helper. E.g. openssl for secure servers
        -S server[:port] Server
        -c rcpt         Cc: recipient. May be multiple
        -e rcpt         Errors-To: recipient

./mail -S kornet.net -s 메일제목 -r 수신자 메일내용.txt

kornet.net --> 220 relay10.kornet.net ESMTP Terrace MailWatcher 5.40.2008012515 (for kornet.net)
kornet.net --> 550 5.1.8 you are not allowed to send mail.
unexpected reply: 550 5.1.8 you are not allowed to send mail.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <getopt.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
 
static char *from_addr  = NULL;                /* 보내는 사람 주소        */
static char *reply_addr = NULL;                /* 받는 사람 주소        */
static char *mailhost   = NULL;                /* 메일서버 주소        */
static int   mailport   = 25;                /* 메일서버 포트        */
static char *subject    = 0;                /* 메일 제목                 */
static FILE *sfp;
static FILE *rfp;
 
/*
** 메일서버에서 응답받기
*/
void Get_Response(void)
{
    char buf[BUFSIZ];
 
    while (fgets(buf, sizeof(buf), rfp)) {
        buf[strlen(buf)-1] = 0;
                /*
        printf("%s --> %s\n", mailhost, buf);
                */
        if (!isdigit(buf[0]) || buf[0] > '3') {
            printf("unexpected reply: %s\n", buf);
            exit(-1);
        }
        if (buf[4] != '-')
            break;
    }
    return;
}
 
/*
** 메일서버로 내용 전송하고 응답받기
*/
void Chat(char *fmt, ...)
{
    va_list ap;
 
    va_start(ap, fmt);
    vfprintf(sfp, fmt, ap);
    va_end(ap);
 
        /*
    va_start(ap, fmt);
    printf("%s <-- \n", mailhost);
    vprintf(fmt, ap);
    va_end(ap);
        */
 
    fflush(sfp);
    Get_Response();
}
 
/*
**  main 함수
*/
 
void Usage(void)
{
        printf("\n");
        printf("usage   : cymail [-S host] [-s subject] <-r reply-addr> FILE\n");
        printf("options :\n");
        /*
        printf("  -S, --smtp-host=HOST        host where MTA can be contacted via SMTP\n")
        */
        printf("          -S,       host where MTA can be contacted via SMTP\n");
        printf("          -s,       subject line of message\n");
        printf("          -r,       address of the sender for replies\n");
        printf("\n");
        exit(0);
}
 
int main(int argc, char **argv)
{
        FILE *fpFile;
    char buf[BUFSIZ];
    char my_name[BUFSIZ];
    struct sockaddr_in sin;
    struct hostent *hp;
    struct servent *sp;
        int c;
    int s;
    int r;
    char *cp;
 
        opterr = 0;
 
        while((c = getopt(argc, argv, "S:s:r:")) != -1)
        {
                switch(c)
                {
                        case 'S':
                                mailhost = optarg;
                                break;
                        case 's':
                                subject = optarg;
                                break;
                        case 'r':
                                from_addr = optarg;
                                reply_addr = optarg;
                                break;
                        case '?':
                                Usage();
                                exit(-1);
                }
        }
 
        if (mailhost == NULL)
        {
                if ((cp = getenv("SMTPSERVER")) != NULL)
                {
                        mailhost = cp;
                }
                else
                {
                        printf("SMTPSERVER is not setting\n");       
                        exit(-1);
                }
        }
 
        if( optind != (argc -1))
        {
                Usage();
                exit(-1);
        }
 
        if(from_addr == NULL)
        {
                Usage();
                exit(-1);
        }
 
    /*
     *  메일 서버에 연결
     */
 
    if ((hp = gethostbyname(mailhost)) == NULL) {
        printf("%s: unknown host\n", mailhost);
        exit(-1);
    }
    if (hp->h_addrtype != AF_INET) {
        printf("unknown address family: %d\n", hp->h_addrtype);
        exit(-1);
    }
 
    memset((char *)&sin, 0, sizeof(sin));
    memcpy((char *)&sin.sin_addr, hp->h_addr, hp->h_length);
 
    sin.sin_family = hp->h_addrtype;
    sin.sin_port = htons(mailport);
 
    if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("socket: error\n");
        exit(-1);
    }
    if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
        printf("connect: error\n");
        exit(-1);
    }
    if ((r = dup(s)) < 0) {
        printf("dup: error\n");
        exit(-1);
    }
    if ((sfp = fdopen(s, "w")) == 0) {
        printf("fdopen: error\n");
        exit(-1);
    }
    if ((rfp = fdopen(r, "r")) == 0) {
        printf("fdopen: error\n");
        exit(-1);
    }
 
    /* 
     *  SMTP 헤더보내기
     */
    Get_Response(); /* 초기 메시지 받기 */
        /*
    Chat("HELO %s\r\n", my_name);
        */
    Chat("MAIL FROM: <%s>\r\n", from_addr);
    Chat("RCPT TO: <%s>\r\n", reply_addr);
    Chat("DATA\r\n");
 
    /* 
     *  메일 제목
     */
        if( subject != NULL)
        {
            fprintf(sfp, "Subject: %s\r\n", subject);
            fprintf(sfp, "\r\n");
    }
 
    /* 
     *  메일 내용 읽기
     */
        if ((fpFile = fopen(argv[argc - 1], "r")) == NULL )
        {
                printf("no message file \n");
                exit(-1);
        }
        else
        {
                while(fgets(buf, sizeof(buf), fpFile))
                {
                        buf[strlen(buf)-1] = 0;
                        if (strcmp(buf, ".") == 0)
                        {
                                fprintf(sfp, ".\r\n");
                        }
                        else
                        {
                                fprintf(sfp, "%s\r\n", buf);
                        }
                }
                fclose(fpFile);
        }
 
    /* 
     *  내용 종료 및 통신 종료
     */
    Chat(".\r\n");
    Chat("QUIT\r\n");
 
        printf("Your mail is sended successfully !!\n");
    exit(0);
}