Mail-Address Check.c

/*-----------------------------------------------------------------------------

mail_addr_check.c (c) 2015 by Siegrist(SystemLoesungen) <PSS @ ZweierNet.ch>

# All Rights reserved.
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

params:    [-v]    verbose to stdout
           mailserverr to connect
           port on server to connect
           email-adress to check
           
returns:   true(1)     if mailaddress exists
           false(0)    else
           
Each command sent to the server is represented in the commands[] array ascending from commands[0] to commands[n].
Fit it to your own taste.
Don't forget the trailing "\r\n", sometimes this is "\n".

Compile with 'gcc -o mail_addr_check mail_addr_check.c'
------------------------------------------------------------------------------

• /

1. include <stdlib.h>
2. include <stdio.h>
3. include <sys/types.h>
4. include <sys/socket.h>
5. include <netinet/in.h>
6. include <netdb.h>
7. include <string.h>
8. include <ctype.h>

1. define VERSION "V0.5"
2. define BUFLEN 1024
3. define TRUE 1
4. define FALSE 0
5. define NUMELEMS(a) (sizeof(a) / sizeof((a)[0]))

int verbose = TRUE; static char *commands[] = { "HELO xy\r\n",

                           "RSET\r\n",
                           "MAIL FROM: mailverification@zweiernet.ch\r\n",
                           "RCPT TO: <__mail_to_check__>\r\n" };

/*-- Subs -------------------------------------- */

void error(char *msg) {

   perror(msg);
   exit(0);

}

void usage(char *prog) {

   fprintf(stderr,"usage %s [-v] < mailserver-to-check-for > < port-on-server-25-or-587 > < email-adress-to-check >\n", prog);
   exit(0);

}

char *replace_str(char *str, char *orig, char *rep) {

   static char bu[BUFLEN];
   char *p;
   
   if(!(p = strstr(str, orig)))
       return str;
   
   strncpy(bu, str, p-str);
   bu[p-str] = '\0';
   sprintf(bu+(p-str), "%s%s", rep, p+strlen(orig));
   
   return bu;

}

/*-- Main -------------------------------------- */

main(int argc, char *argv[]) {

   register int    sockfd;
   register int    n;
   register int    indx;
   register int    i, j;
   int             port;
   struct          sockaddr_in serv_addr;
   struct          hostent *server;
   struct          in_addr *p;
   unsigned char   *mail_to_check, *ret;
   unsigned char   buffer[BUFLEN];
   
   setbuf(stdout, NULL);   // flush stdout
   
   /*-- program args */
   i = 1;
   if (argc < 4)
       usage(argv[0]);
   
   if (argc == 5) { 
       if (strcmp(argv[i], "-v") == 0) { 
           verbose = TRUE;
           i++;
       } else usage(argv[0]);
   }
   server = gethostbyname(argv[i]); i++;
   if ( server == NULL) 
       error("unknown host.");
   port = atoi(argv[i]); i++;
   memcpy((char *)&mail_to_check, &argv[i], sizeof(argv[i]));
   
   /*-- create socket */
   if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
       error("ERROR opening socket");
   
   /*-- connect to server */
   bzero((char *) &serv_addr, sizeof(serv_addr));
   memcpy((char *)&serv_addr.sin_addr, server->h_addr, server->h_length);
   serv_addr.sin_family    = AF_INET;
   serv_addr.sin_port      = htons((u_short)port);
   
   if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) 
       error("ERROR connecting");
   
   bzero(buffer, BUFLEN); 
   if (n = recv(sockfd, buffer, BUFLEN, 0) < 0)
        error("ERROR reading from socket");
   if (verbose) printf("%s\n", buffer);
   
   /*-- write n read to/from socket*/
   indx=0;
   while ( indx < NUMELEMS(commands) ) {
       char * ret = replace_str(commands[indx], "__mail_to_check__", mail_to_check);
       if (verbose) printf("%s", ret);
       if (n = send(sockfd, ret, strlen(ret), 0) < 0 )
           error("ERROR writing to socket");
       bzero(buffer, BUFLEN);
       if ( n = recv(sockfd, buffer, BUFLEN, 0) < 0 )
           error("ERROR reading from socket");
       if (verbose) printf("%s\n",buffer);
       indx++;
   }
   
   /*-- return value and exit */
   for (j = strlen(buffer)-5; buffer[j]; j++) buffer[j] = tolower(buffer[j]);
   if (strstr(buffer, "ok") != NULL) {
       if (verbose) printf("OK\n");
       exit(TRUE);
   } else {
       if (verbose) printf("NOK\n");
       exit(FALSE);
   }
   

} ......