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			 fetchmail README

fetchmail is a free, full-featured, robust, well-documented remote
mail retrieval and forwarding utility intended to be used over
on-demand TCP/IP links (such as SLIP or PPP connections).  It
retrieves mail from remote mail servers and forwards it to your local
(client) machine's delivery system, so it can then be be read by
normal mail user agents such as elm(1) or Mail(1).

fetchmail supports standard all mail-retrieval protocols in use on the
Internet: POP2, POP3 (including POP3 with RFC1938 one-time passwords),
RPOP, APOP, KPOP, Compuserve's POP3 with RPA, all flavors of IMAP
(including IMAP4rev1 with RFC1731 Kerberos v4  or GSSAPI authentication),
and ESMTP ETRN.

The fetchmail code was developed under Linux, but has also been
extensively tested under 4.4BSD, AIX, HP-UX versions 9 and 10, 
SunOS, Solaris, NEXTSTEP, and OSF 3.2.  

It should be readily portable to other Unix variants (it uses GNU
autoconf).  It has also been ported to QNX; to build under QNX, see
the header comments in the Makefile.  It is reported to build and run
under AmigaOS.

A beta OS/2 port of fetchmail is available from Jason F. McBrayer at 
http://studentweb.tulane.edu/%7Ejmcbray/os2.

See the distribution files FEATURES for a full list of features, NEWS
for detailed information on recent changes and NOTES for design notes.

The fetchmail code appears to be stable and free of bugs affecting
normal operation (that is, retrieving from POP3 or IMAP in single-drop
mode and forwarding via SMTP to sendmail).  It will probably undergo
substantial change only if and when support for a new retrieval
protocol or authentication mode is added.

You can easily fetch the latest version of fetchmail via FTP from the
following FTP directory:

	ftp://ftp.ccil.org/pub/esr/fetchmail

Or you can get it from the fetchmail home page:

	http://www.ccil.org/~esr/fetchmail

Enjoy!

							-- esr
generated by cgit v1.2.3 (git 2.46.0) at 2026-02-24 23:40:18 +0000
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/*
 * checkalias.c -- check to see if two hostnames or IP addresses are equivalent
 *
 * Copyright 1997 by Eric S. Raymond
 * For license terms, see the file COPYING in this directory.
 */
#include "config.h"
#ifdef HAVE_GETHOSTBYNAME
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#ifdef HAVE_NET_SOCKET_H
#include <net/socket.h>
#else
#include <sys/socket.h>
#endif
#include <netinet/in.h>
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#include <netdb.h>
#include "i18n.h"
#include "mx.h"
#include "fetchmail.h"

#define MX_RETRIES	3

static int is_ip_alias(const char *name1,const char *name2)
/*
 * Given two hostnames as arguments, returns TRUE if they
 * have at least one IP address in common.
 * No check is done on errors returned by gethostbyname,
 * the calling function does them.
 */
{
    typedef unsigned char address_t[sizeof (struct in_addr)]; 
    typedef struct _address_e
    {
	struct _address_e *next;
	address_t address;
    } 
    address_e;
    address_e *host_a_addr=0, *host_b_addr=0;	/* assignments pacify -Wall */
    address_e *dummy_addr;

    int i;
    struct hostent *hp;
    char **p;
 
    hp = gethostbyname(name1);
 
    dummy_addr = (address_e *)NULL;

    for (i=0,p = hp->h_addr_list; *p != 0; i++,p++)
    {
	struct in_addr in;
	(void) memcpy(&in.s_addr, *p, sizeof (in.s_addr));
	xalloca(host_a_addr, address_e *, sizeof (address_e));
	memset (host_a_addr,0, sizeof (address_e));
	host_a_addr->next = dummy_addr;
	(void) memcpy(&host_a_addr->address, *p, sizeof (in.s_addr));
	dummy_addr = host_a_addr;
    }

    hp = gethostbyname(name2);

    dummy_addr = (address_e *)NULL;
    for (i=0,p = hp->h_addr_list; *p != 0; i++,p++)
    {
	struct in_addr in;
	(void) memcpy(&in.s_addr, *p, sizeof (in.s_addr));
	xalloca(host_b_addr, address_e *, sizeof (address_e));
	memset (host_b_addr,0, sizeof (address_e));
	host_b_addr->next = dummy_addr;
	(void) memcpy(&host_b_addr->address, *p, sizeof (in.s_addr));
	dummy_addr = host_b_addr;
    }

    while (host_a_addr)
    {
	while (host_b_addr)
	{
	    if (!memcmp(host_b_addr->address,host_a_addr->address, sizeof (address_t)))
		return (TRUE);

	    host_b_addr = host_b_addr->next;
	}
	host_a_addr = host_a_addr->next;
    }
    return (FALSE);
}

int is_host_alias(const char *name, struct query *ctl)
/* determine whether name is a DNS alias of the mailserver for this query */
{
    struct hostent	*he,*he_st;
    struct mxentry	*mxp, *mxrecords;
    struct idlist	*idl;
    int			namelen;

    struct hostdata *lead_server = 
	ctl->server.lead_server ? ctl->server.lead_server : &ctl->server;

    /*
     * The first two checks are optimizations that will catch a good
     * many cases.
     *
     * (1) check against the `true name' deduced from the poll label
     * and the via option (if present) at the beginning of the poll cycle.  
     * Odds are good this will either be the mailserver's FQDN or a suffix of
     * it with the mailserver's domain's default host name omitted.
     *
     * (2) Then check the rest of the `also known as'
     * cache accumulated by previous DNS checks.  This cache is primed
     * by the aka list option.
     *
     * Any of these on a mail address is definitive.  Only if the
     * name doesn't match any is it time to call the bind library.
     * If this happens odds are good we're looking at an MX name.
     */
    if (strcasecmp(lead_server->truename, name) == 0)
	return(TRUE);
    else if (str_in_list(&lead_server->akalist, name, TRUE))
	return(TRUE);
    else if (!ctl->server.dns)
	return(FALSE);

    /*
     * Now check for a suffix match on the akalist.  The theory here is
     * that if the user says `aka netaxs.com', we actually want to match
     * foo.netaxs.com and bar.netaxs.com.
     */
    namelen = strlen(name);
    for (idl = lead_server->akalist; idl; idl = idl->next)
    {
	char	*ep;

	/*
	 * Test is >= here because str_in_list() should have caught the
	 * equal-length case above.  Doing it this way guarantees that
	 * ep[-1] is a valid reference.
	 */
	if (strlen(idl->id) >= namelen)
	    continue;
	ep = (char *)name + (namelen - strlen(idl->id));
	/* a suffix led by . must match */
	if (ep[-1] == '.' && !strcmp(ep, idl->id))
	    return(TRUE);
    }

#ifndef HAVE_RES_SEARCH
    return(FALSE);
#else
    /*
     * The only code that calls the BIND library is here and in the
     * start-of-run probe with gethostbyname(3) under ETRN/Kerberos.
     *
     * We know DNS service was up at the beginning of the run.
     * If it's down, our nameserver has crashed.  We don't want to try
     * delivering the current message or anything else from the
     * current server until it's back up.
     */
    if ((he = gethostbyname(name)) != (struct hostent *)NULL)
    {
	if (strcasecmp(ctl->server.truename, he->h_name) == 0)
	    goto match;
        else if (((he_st = gethostbyname(ctl->server.truename)) != (struct hostent *)NULL) && ctl->server.checkalias)
	{
	    if (outlevel >= O_DEBUG)
		report(stdout, _("Checking if %s is really the same node as %s\n"),ctl->server.truename,name);
	    if (is_ip_alias(ctl->server.truename,name) == TRUE)
	    {
		if (outlevel >= O_DEBUG)
		    report(stdout, _("Yes, their IP addresses match\n"));
		goto match;
	    }
	    if (outlevel >= O_DEBUG)
		report(stdout, _("No, their IP addresses don't match\n"));
	    return(FALSE);
	}
	else
	    return(FALSE);
    }
    else
	switch (h_errno)
	{
	case HOST_NOT_FOUND:	/* specified host is unknown */
#ifndef __BEOS__
	case NO_ADDRESS:	/* valid, but does not have an IP address */
	    break;
#endif
	case NO_RECOVERY:	/* non-recoverable name server error */
	case TRY_AGAIN:		/* temporary error on authoritative server */
	default:
	    if (outlevel != O_SILENT)
		report_complete(stdout, "\n");	/* terminate the progress message */
	    report(stderr,
		_("nameserver failure while looking for `%s' during poll of %s.\n"),
		name, ctl->server.pollname);
	    ctl->errcount++;
	    break;
	}

    /*
     * We're only here if DNS was OK but the gethostbyname() failed
     * with a HOST_NOT_FOUND or NO_ADDRESS error.
     * Search for a name match on MX records pointing to the server.
     */
    h_errno = 0;
    if ((mxrecords = getmxrecords(name)) == (struct mxentry *)NULL)
    {
	switch (h_errno)
	{
	case HOST_NOT_FOUND:	/* specified host is unknown */
#ifndef __BEOS__
	case NO_ADDRESS:	/* valid, but does not have an IP address */
	    return(FALSE);
	    break;
#endif
	case NO_RECOVERY:	/* non-recoverable name server error */
	case TRY_AGAIN:		/* temporary error on authoritative server */
	default:
	    report(stderr,
		_("nameserver failure while looking for `%s' during poll of %s.\n"),
		name, ctl->server.pollname);
	    ctl->errcount++;
	    break;
	}
    }
    else
    {
	for (mxp = mxrecords; mxp->name; mxp++)
	    if (strcasecmp(ctl->server.truename, mxp->name) == 0)
		goto match;
	return(FALSE);
    match:;
    }

    /* add this name to relevant server's `also known as' list */
    save_str(&lead_server->akalist, name, 0);
    return(TRUE);
#endif /* HAVE_RES_SEARCH */
}
#endif /* HAVE_GETHOSTBYNAME */

/* checkalias.c ends here */
generated by cgit v1.2.3 (git 2.46.0) at 2026-02-24 23:40:16 +0000