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'
 ------------------------------------------------------------------------------
*/
 
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 
#include <string.h>
#include <ctype.h>
 
#define VERSION		"V0.5"
#define BUFLEN 		1024
#define TRUE 		1
#define FALSE 		0
#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);
	}
 
}