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); }

}