mailsrvr.c

/* mailsrvr.c */

/* Synchronet Mail (SMTP/POP3) server and sendmail threads */

/* $Id$ */

/****************************************************************************
 * @format.tab-size 4		(Plain Text/Source Code File Header)			*
 * @format.use-tabs true	(see http://www.synchro.net/ptsc_hdr.html)		*
 *																			*
 * Copyright 2005 Rob Swindell - http://www.synchro.net/copyright.html		*
 *																			*
 * 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; either version 2			*
 * of the License, or (at your option) any later version.					*
 * See the GNU General Public License for more details: gpl.txt or			*
 * http://www.fsf.org/copyleft/gpl.html										*
 *																			*
 * Anonymous FTP access to the most recent released source is available at	*
 * ftp://vert.synchro.net, ftp://cvs.synchro.net and ftp://ftp.synchro.net	*
 *																			*
 * Anonymous CVS access to the development source and modification history	*
 * is available at cvs.synchro.net:/cvsroot/sbbs, example:					*
 * cvs -d :pserver:anonymous@cvs.synchro.net:/cvsroot/sbbs login			*
 *     (just hit return, no password is necessary)							*
 * cvs -d :pserver:anonymous@cvs.synchro.net:/cvsroot/sbbs checkout src		*
 *																			*
 * For Synchronet coding style and modification guidelines, see				*
 * http://www.synchro.net/source.html										*
 *																			*
 * You are encouraged to submit any modifications (preferably in Unix diff	*
 * format) via e-mail to mods@synchro.net									*
 *																			*
 * Note: If this box doesn't appear square, then you need to fix your tabs.	*
 ****************************************************************************/

/* Platform-specific headers */
#ifdef _WIN32

	#include <io.h>			/* open/close */
	#include <share.h>		/* share open flags */
	#include <process.h>	/* _beginthread */
	#include <windows.h>	/* required for mmsystem.h */
	#include <mmsystem.h>	/* SND_ASYNC */

#endif


/* ANSI C Library headers */
#include <stdio.h>
#include <stdlib.h>			/* ltoa in GNU C lib */
#include <stdarg.h>			/* va_list */
#include <string.h>			/* strrchr */
#include <ctype.h>			/* isdigit */
#include <fcntl.h>			/* Open flags */
#include <errno.h>			/* errno */

/* Synchronet-specific headers */
#undef SBBS	/* this shouldn't be defined unless building sbbs.dll/libsbbs.so */
#include "sbbs.h"
#include "mailsrvr.h"
#include "mime.h"
#include "md5.h"
#include "crc32.h"
#include "base64.h"
#include "ini_file.h"

/* Constants */
#define FORWARD			"forward:"
#define NO_FORWARD		"local:"

int dns_getmx(char* name, char* mx, char* mx2
			  ,DWORD intf, DWORD ip_addr, BOOL use_tcp, int timeout);

static char* pop_err	=	"-ERR";
static char* ok_rsp		=	"250 OK";
static char* auth_ok	=	"235 User Authenticated";
static char* sys_error	=	"421 System error";
static char* sys_unavail=	"421 System unavailable, try again later";
static char* badarg_rsp =	"501 Bad argument";
static char* badseq_rsp	=	"503 Bad sequence of commands";
static char* badauth_rsp=	"535 Authentication failure";
static char* badrsp_err	=	"%s replied with:\r\n\"%s\"\r\n"
							"instead of the expected reply:\r\n\"%s ...\"";

#define TIMEOUT_THREAD_WAIT		60		/* Seconds */
#define DNSBL_THROTTLE_VALUE	5000	/* Milliseconds */

#define STATUS_WFC	"Listening"

static mail_startup_t* startup=NULL;
static scfg_t	scfg;
static SOCKET	server_socket=INVALID_SOCKET;
static SOCKET	pop3_socket=INVALID_SOCKET;
static DWORD	active_clients=0;
static int		active_sendmail=0;
static DWORD	thread_count=0;
static BOOL		sendmail_running=FALSE;
static DWORD	sockets=0;
static DWORD	served=0;
static BOOL		terminate_server=FALSE;
static BOOL		terminate_sendmail=FALSE;
static sem_t	sendmail_wakeup_sem;
static char		revision[16];
static time_t	uptime;
static str_list_t recycle_semfiles;
static str_list_t shutdown_semfiles;
static int		mailproc_count;

struct mailproc {
	char		cmdline[INI_MAX_VALUE_LEN];
	str_list_t	to;
	BOOL		passthru;
	BOOL		native;
} *mailproc_list;

typedef struct {
	SOCKET			socket;
	SOCKADDR_IN		client_addr;
} smtp_t,pop3_t;

static int lprintf(int level, char *fmt, ...)
{
	va_list argptr;
	char sbuf[1024];

    if(startup==NULL || startup->lputs==NULL)
        return(0);

	va_start(argptr,fmt);
    vsnprintf(sbuf,sizeof(sbuf),fmt,argptr);
	sbuf[sizeof(sbuf)-1]=0;
    va_end(argptr);
    return(startup->lputs(startup->cbdata,level,sbuf));
}

#ifdef _WINSOCKAPI_

static WSADATA WSAData;
#define SOCKLIB_DESC WSAData.szDescription
static BOOL WSAInitialized=FALSE;

static BOOL winsock_startup(void)
{
	int		status;             /* Status Code */

    if((status = WSAStartup(MAKEWORD(1,1), &WSAData))==0) {
		lprintf(LOG_INFO,"%s %s",WSAData.szDescription, WSAData.szSystemStatus);
		WSAInitialized=TRUE;
		return (TRUE);
	}

    lprintf(LOG_CRIT,"!WinSock startup ERROR %d", status);
	return (FALSE);
}

#else /* No WINSOCK */

#define winsock_startup()	(TRUE)
#define SOCKLIB_DESC NULL

#endif

static void update_clients(void)
{
	if(startup!=NULL && startup->clients!=NULL)
		startup->clients(startup->cbdata,active_clients+active_sendmail);
}

static void client_on(SOCKET sock, client_t* client, BOOL update)
{
	if(startup!=NULL && startup->client_on!=NULL)
		startup->client_on(startup->cbdata,TRUE,sock,client,update);
}

static void client_off(SOCKET sock)
{
	if(startup!=NULL && startup->client_on!=NULL)
		startup->client_on(startup->cbdata,FALSE,sock,NULL,FALSE);
}

static void thread_up(BOOL setuid)
{
	thread_count++;
	if(startup!=NULL && startup->thread_up!=NULL)
		startup->thread_up(startup->cbdata,TRUE,setuid);
}

static void thread_down(void)
{
	if(thread_count>0)
		thread_count--;
	if(startup!=NULL && startup->thread_up!=NULL)
		startup->thread_up(startup->cbdata,FALSE,FALSE);
}

SOCKET mail_open_socket(int type)
{
	char	error[256];
	SOCKET	sock;

	sock=socket(AF_INET, type, IPPROTO_IP);
	if(sock!=INVALID_SOCKET && startup!=NULL && startup->socket_open!=NULL) 
		startup->socket_open(startup->cbdata,TRUE);
	if(sock!=INVALID_SOCKET) {
		if(set_socket_options(&scfg, sock,error))
			lprintf(LOG_ERR,"%04d !ERROR %s",sock,error);

		sockets++;
#if 0 /*def _DEBUG */
		lprintf(LOG_DEBUG,"%04d Socket opened (%d sockets in use)",sock,sockets);
#endif
	}
	return(sock);
}

int mail_close_socket(SOCKET sock)
{
	int		result;

	if(sock==INVALID_SOCKET)
		return(-1);

	shutdown(sock,SHUT_RDWR);	/* required on Unix */
	result=closesocket(sock);
	if(startup!=NULL && startup->socket_open!=NULL)
		startup->socket_open(startup->cbdata,FALSE);
	sockets--;
	if(result!=0) {
		if(ERROR_VALUE!=ENOTSOCK)
			lprintf(LOG_ERR,"%04d !ERROR %d closing socket",sock, ERROR_VALUE);
	}
#if 0 /*def _DEBUG */
	else 
		lprintf(LOG_DEBUG,"%04d Socket closed (%d sockets in use)",sock,sockets);
#endif

	return(result);
}

static void status(char* str)
{
	if(startup!=NULL && startup->status!=NULL)
	    startup->status(startup->cbdata,str);
}

int sockprintf(SOCKET sock, char *fmt, ...)
{
	int		len;
	int		maxlen;
	int		result;
	va_list argptr;
	char	sbuf[1024];
	fd_set	socket_set;
	struct timeval tv;

    va_start(argptr,fmt);
    len=vsnprintf(sbuf,maxlen=sizeof(sbuf)-2,fmt,argptr);
    va_end(argptr);

	if(len<0 || len > maxlen) /* format error or output truncated */
		len=maxlen;
	if(startup->options&MAIL_OPT_DEBUG_TX)
		lprintf(LOG_DEBUG,"%04d TX: %.*s", sock, len, sbuf);
	memcpy(sbuf+len,"\r\n",2);
	len+=2;

	if(sock==INVALID_SOCKET) {
		lprintf(LOG_WARNING,"!INVALID SOCKET in call to sockprintf");
		return(0);
	}

	/* Check socket for writability (using select) */
	tv.tv_sec=300;
	tv.tv_usec=0;

	FD_ZERO(&socket_set);
	FD_SET(sock,&socket_set);

	if((result=select(sock+1,NULL,&socket_set,NULL,&tv))<1) {
		if(result==0)
			lprintf(LOG_NOTICE,"%04d !TIMEOUT selecting socket for send"
				,sock);
		else
			lprintf(LOG_NOTICE,"%04d !ERROR %d selecting socket for send"
				,sock, ERROR_VALUE);
		return(0);
	}

	while((result=sendsocket(sock,sbuf,len))!=len) {
		if(result==SOCKET_ERROR) {
			if(ERROR_VALUE==EWOULDBLOCK) {
				YIELD();
				continue;
			}
			if(ERROR_VALUE==ECONNRESET) 
				lprintf(LOG_NOTICE,"%04d Connection reset by peer on send",sock);
			else if(ERROR_VALUE==ECONNABORTED) 
				lprintf(LOG_NOTICE,"%04d Connection aborted by peer on send",sock);
			else
				lprintf(LOG_NOTICE,"%04d !ERROR %d sending on socket",sock,ERROR_VALUE);
			return(0);
		}
		lprintf(LOG_WARNING,"%04d !ERROR: short send on socket: %d instead of %d",sock,result,len);
	}
	return(len);
}

static time_t checktime(void)
{
	struct tm tm;

    memset(&tm,0,sizeof(tm));
    tm.tm_year=94;
    tm.tm_mday=1;
    return(mktime(&tm)-0x2D24BD00L);
}

static void recverror(SOCKET socket, int rd, int line)
{
	if(rd==0) 
		lprintf(LOG_NOTICE,"%04d Socket closed by peer on receive (line %d)"
			,socket, line);
	else if(rd==SOCKET_ERROR) {
		if(ERROR_VALUE==ECONNRESET) 
			lprintf(LOG_NOTICE,"%04d Connection reset by peer on receive (line %d)"
				,socket, line);
		else if(ERROR_VALUE==ECONNABORTED) 
			lprintf(LOG_NOTICE,"%04d Connection aborted by peer on receive (line %d)"
				,socket, line);
		else
			lprintf(LOG_NOTICE,"%04d !ERROR %d receiving on socket (line %d)"
				,socket, ERROR_VALUE, line);
	} else
		lprintf(LOG_WARNING,"%04d !ERROR: recv on socket returned unexpected value: %d (line %d)"
			,socket, rd, line);
}


static int sockreadline(SOCKET socket, char* buf, int len)
{
	char	ch;
	int		i,rd=0;
	fd_set	socket_set;
	struct	timeval	tv;
	time_t	start;

	buf[0]=0;

	start=time(NULL);

	if(socket==INVALID_SOCKET) {
		lprintf(LOG_WARNING,"!INVALID SOCKET in call to sockreadline");
		return(-1);
	}
	
	while(rd<len-1) {

		if(server_socket==INVALID_SOCKET || terminate_server) {
			lprintf(LOG_WARNING,"%04d !ABORTING sockreadline",socket);
			return(-1);
		}

		tv.tv_sec=startup->max_inactivity;
		tv.tv_usec=0;

		FD_ZERO(&socket_set);
		FD_SET(socket,&socket_set);

		i=select(socket+1,&socket_set,NULL,NULL,&tv);

		if(i<1) {
			if(i==0) {
				if((time(NULL)-start)>startup->max_inactivity) {
					lprintf(LOG_WARNING,"%04d !SOCKET INACTIVE",socket);
					return(-1);
				}
				continue;
			}
			recverror(socket,i,__LINE__);
			return(-1);
		}
		i=recv(socket, &ch, 1, 0);
		if(i<1) {
			recverror(socket,i,__LINE__);
			return(-1);
		}
		if(ch=='\n' /* && rd>=1 */ ) { /* Mar-9-2003: terminate on sole LF */
			break;
		}	
		buf[rd++]=ch;
	}
	if(rd>0 && buf[rd-1]=='\r')
		rd--;
	buf[rd]=0;
	
	return(rd);
}

static BOOL sockgetrsp(SOCKET socket, char* rsp, char *buf, int len)
{
	int rd;

	while(1) {
		rd = sockreadline(socket, buf, len);
		if(rd<1) 
			return(FALSE);
		if(buf[3]=='-')	{ /* Multi-line response */
			if(startup->options&MAIL_OPT_DEBUG_RX_RSP) 
				lprintf(LOG_DEBUG,"%04d RX: %s",socket,buf);
			continue;
		}
		if(rsp!=NULL && strnicmp(buf,rsp,strlen(rsp))) {
			lprintf(LOG_WARNING,"%04d !INVALID RESPONSE: '%s' Expected: '%s'", socket, buf, rsp);
			return(FALSE);
		}
		break;
	}
	if(startup->options&MAIL_OPT_DEBUG_RX_RSP) 
		lprintf(LOG_DEBUG,"%04d RX: %s",socket,buf);
	return(TRUE);
}

#define MAX_LINE_LEN	1000

static ulong sockmsgtxt(SOCKET socket, smbmsg_t* msg, char* msgtxt, ulong maxlines)
{
	char		toaddr[256]="";
	char		fromaddr[256]="";
	char		fromhost[256];
	char		date[64];
	char		filepath[MAX_PATH+1]="";
	char*		p;
	char*		tp;
	char*		boundary=NULL;
	char*		content_type=NULL;
	int			i;
	int			s;
	ulong		lines;

	/* HEADERS (in recommended order per RFC822 4.1) */
	if(!sockprintf(socket,"Date: %s",msgdate(msg->hdr.when_written,date)))
		return(0);

	if((p=smb_get_hfield(msg,RFC822FROM,NULL))!=NULL)
		s=sockprintf(socket,"From: %s",p);	/* use original RFC822 header field */
	else {
		if(msg->from_net.type==NET_INTERNET && msg->from_net.addr!=NULL)
			SAFECOPY(fromaddr,(char*)msg->from_net.addr);
		else if(msg->from_net.type==NET_QWK && msg->from_net.addr!=NULL)
			SAFEPRINTF2(fromaddr,"%s!%s"
				,(char*)msg->from_net.addr
				,usermailaddr(&scfg,fromhost,msg->from));
		else 
			usermailaddr(&scfg,fromaddr,msg->from);
		if(fromaddr[0]=='<')
			s=sockprintf(socket,"From: \"%s\" %s",msg->from,fromaddr);
		else
			s=sockprintf(socket,"From: \"%s\" <%s>",msg->from,fromaddr);
	}
	if(!s)
		return(0);

	if(msg->from_org!=NULL || msg->from_net.type==NET_NONE)
		if(!sockprintf(socket,"Organization: %s"
			,msg->from_org==NULL ? scfg.sys_name : msg->from_org))
			return(0);

	if(!sockprintf(socket,"Subject: %s",msg->subj))
		return(0);

	if((p=smb_get_hfield(msg,RFC822TO,NULL))!=NULL)
		s=sockprintf(socket,"To: %s",p);	/* use original RFC822 header field */
	else {
		if(strchr(msg->to,'@')!=NULL || msg->to_net.addr==NULL)
			s=sockprintf(socket,"To: %s",msg->to);	/* Avoid double-@ */
		else if(msg->to_net.type==NET_INTERNET || msg->to_net.type==NET_QWK) {
			if(strchr((char*)msg->to_net.addr,'<')!=NULL)
				s=sockprintf(socket,"To: %s",(char*)msg->to_net.addr);
			else
				s=sockprintf(socket,"To: \"%s\" <%s>",msg->to,(char*)msg->to_net.addr);
		} else {
			usermailaddr(&scfg,toaddr,msg->to);
			s=sockprintf(socket,"To: \"%s\" <%s>",msg->to,toaddr);
		}
	}
	if(!s)
		return(0);
	if((p=smb_get_hfield(msg,RFC822REPLYTO,NULL))==NULL) {
		if(msg->replyto_net.type==NET_INTERNET)
			p=msg->replyto_net.addr;
		else if(msg->replyto!=NULL)
			p=msg->replyto;
	}
	if(p!=NULL)
		s=sockprintf(socket,"Reply-To: %s",p);	/* use original RFC822 header field */
	if(!s)
		return(0);
	if(!sockprintf(socket,"Message-ID: %s",get_msgid(&scfg,INVALID_SUB,msg)))
		return(0);
	if(msg->reply_id!=NULL)
		if(!sockprintf(socket,"In-Reply-To: %s",msg->reply_id))
			return(0);
    for(i=0;i<msg->total_hfields;i++) { 
		if(msg->hfield[i].type==RFC822HEADER) { 
			if(strnicmp((char*)msg->hfield_dat[i],"Content-Type:",13)==0)
				content_type=msg->hfield_dat[i];
			if(!sockprintf(socket,"%s",(char*)msg->hfield_dat[i]))
				return(0);
        } else if(msg->hdr.auxattr&MSG_FILEATTACH && msg->hfield[i].type==FILEATTACH) 
            strncpy(filepath,(char*)msg->hfield_dat[i],sizeof(filepath)-1);
    }
	/* Default MIME Content-Type for non-Internet messages */
	if(msg->from_net.type!=NET_INTERNET && content_type==NULL) {
		/* No content-type specified, so assume IBM code-page 437 (full ex-ASCII) */
		sockprintf(socket,"Content-Type: text/plain; charset=IBM437");
		sockprintf(socket,"Content-Transfer-Encoding: 8bit");
	}

	if(msg->hdr.auxattr&MSG_FILEATTACH) {
		if(filepath[0]==0) { /* filename stored in subject */
			if(msg->idx.to!=0)
				snprintf(filepath,sizeof(filepath)-1,"%sfile/%04u.in/%s"
					,scfg.data_dir,msg->idx.to,msg->subj);
			else
				snprintf(filepath,sizeof(filepath)-1,"%sfile/%04u.out/%s"
					,scfg.data_dir,msg->idx.from,msg->subj);
		}
        boundary=mimegetboundary();
        mimeheaders(socket,boundary);
        sockprintf(socket,"");
        mimeblurb(socket,boundary);
        sockprintf(socket,"");
        mimetextpartheader(socket,boundary);
	}
	if(!sockprintf(socket,""))	/* Header Terminator */
		return(0);

	/* MESSAGE BODY */
	lines=0;
#if 0	/* This is now handled in smb_getmsgtxt() */
    for(i=0;i<msg->total_hfields;i++) {			/* delivery failure notification? */
		if(msg->hfield[i].type==SMTPSYSMSG || msg->hfield[i].type==SMB_COMMENT) { 
			if(!sockprintf(socket,"%s",(char*)msg->hfield_dat[i]))
				return(0);
			lines++;
		}
    }
#endif
	p=msgtxt;
	while(*p && lines<maxlines) {
		tp=strchr(p,'\n');
		if(tp) {
			if(tp-p>MAX_LINE_LEN)
				tp=p+MAX_LINE_LEN;
			*tp=0;
		}
		truncsp(p);	/* Takes care of '\r' or spaces */
		if(*p=='.')
			i=sockprintf(socket,".%.*s",MAX_LINE_LEN,p);
		else
			i=sockprintf(socket,"%.*s",MAX_LINE_LEN,p);
		if(!i)
			break;
		if(tp==NULL)
			break;
		p=tp+1;
		lines++;
		/* release time-slices every x lines */
		if(startup->lines_per_yield
			&& !(lines%startup->lines_per_yield))	
			YIELD();
	}
    if(msg->hdr.auxattr&MSG_FILEATTACH) { 
	    sockprintf(socket,"");
		lprintf(LOG_INFO,"%04u MIME Encoding and sending %s",socket,filepath);
        if(!mimeattach(socket,boundary,filepath))
			lprintf(LOG_ERR,"%04u !ERROR opening/encoding/sending %s",socket,filepath);
		else {
			endmime(socket,boundary);
			if(msg->hdr.auxattr&MSG_KILLFILE)
				if(remove(filepath)!=0)
					lprintf(LOG_WARNING,"%04u !ERROR %d removing %s",socket,filepath);
		}
    }
    sockprintf(socket,".");	/* End of text */
    if(boundary) FREE(boundary);
	return(lines);
}

static u_long resolve_ip(char *inaddr)
{
	char*		p;
	char*		addr;
	char		buf[128];
	HOSTENT*	host;

	SAFECOPY(buf,inaddr);
	addr=buf;
	if(*addr=='[' && *(p=lastchar(addr))==']') { /* Support [ip_address] notation */
		addr++;
		*p=0;
	}

	if(*addr==0)
		return((u_long)INADDR_NONE);

	for(p=addr;*p;p++)
		if(*p!='.' && !isdigit(*p))
			break;
	if(!(*p))
		return(inet_addr(addr));

	if((host=gethostbyname(inaddr))==NULL) {
		lprintf(LOG_WARNING,"0000 !ERROR resolving hostname: %s",inaddr);
		return((u_long)INADDR_NONE);
	}
	return(*((ulong*)host->h_addr_list[0]));
}


static void pop3_thread(void* arg)
{
	char*		p;
	char		str[128];
	char		buf[512];
	char		host_name[128];
	char		host_ip[64];
	char		username[LEN_ALIAS+1];
	char		password[LEN_PASS+1];
	char		challenge[256];
	char		digest[MD5_DIGEST_SIZE];
	char*		response="";
	char*		msgtxt;
	int			i;
	int			rd;
	BOOL		activity=FALSE;
	BOOL		apop=FALSE;
	long		l;
	ulong		lines;
	ulong		lines_sent;
	long		msgs,msgnum;
	ulong		bytes;
	SOCKET		socket;
	HOSTENT*	host;
	smb_t		smb;
	smbmsg_t	msg;
	user_t		user;
	client_t	client;
	mail_t*		mail;
	pop3_t		pop3=*(pop3_t*)arg;

	thread_up(TRUE /* setuid */);

	free(arg);

	socket=pop3.socket;

	if(startup->options&MAIL_OPT_DEBUG_POP3)
		lprintf(LOG_DEBUG,"%04d POP3 session thread started", socket);

#ifdef _WIN32
	if(startup->pop3_sound[0] && !(startup->options&MAIL_OPT_MUTE)) 
		PlaySound(startup->pop3_sound, NULL, SND_ASYNC|SND_FILENAME);
#endif

	SAFECOPY(host_ip,inet_ntoa(pop3.client_addr.sin_addr));

	if(startup->options&MAIL_OPT_DEBUG_POP3)
		lprintf(LOG_INFO,"%04d POP3 connection accepted from: %s port %u"
			,socket, host_ip, ntohs(pop3.client_addr.sin_port));

	if(startup->options&MAIL_OPT_NO_HOST_LOOKUP)
		host=NULL;
	else
		host=gethostbyaddr((char *)&pop3.client_addr.sin_addr
			,sizeof(pop3.client_addr.sin_addr),AF_INET);

	if(host!=NULL && host->h_name!=NULL)
		SAFECOPY(host_name,host->h_name);
	else
		strcpy(host_name,"<no name>");

	if(startup->options&MAIL_OPT_DEBUG_POP3
		&& !(startup->options&MAIL_OPT_NO_HOST_LOOKUP)) {
		lprintf(LOG_INFO,"%04d POP3 Hostname: %s", socket, host_name);
		for(i=0;host!=NULL && host->h_aliases!=NULL && host->h_aliases[i]!=NULL;i++)
			lprintf(LOG_INFO,"%04d POP3 HostAlias: %s", socket, host->h_aliases[i]);
	}

	if(trashcan(&scfg,host_ip,"ip")) {
		lprintf(LOG_NOTICE,"%04d !POP3 BLOCKED CLIENT IP ADDRESS: %s"
			,socket, host_ip);
		sockprintf(socket,"-ERR Access denied.");
		mail_close_socket(socket);
		thread_down();
		return;
	}

	if(trashcan(&scfg,host_name,"host")) {
		lprintf(LOG_NOTICE,"%04d !POP3 BLOCKED CLIENT HOSTNAME: %s"
			,socket, host_name);
		sockprintf(socket,"-ERR Access denied.");
		mail_close_socket(socket);
		thread_down();
		return;
	}

	active_clients++, update_clients();

	/* Initialize client display */
	client.size=sizeof(client);
	client.time=time(NULL);
	SAFECOPY(client.addr,host_ip);
	SAFECOPY(client.host,host_name);
	client.port=ntohs(pop3.client_addr.sin_port);
	client.protocol="POP3";
	client.user="<unknown>";
	client_on(socket,&client,FALSE /* update */);

	SAFEPRINTF(str,"POP3: %s", host_ip);
	status(str);

	mail=NULL;

	do {
		memset(&smb,0,sizeof(smb));
		memset(&msg,0,sizeof(msg));
		memset(&user,0,sizeof(user));
		password[0]=0;

		srand(time(NULL));	/* seed random number generator */
		rand();	/* throw-away first result */
		safe_snprintf(challenge,sizeof(challenge),"<%x%x%lx%lx@%.128s>"
			,rand(),socket,(ulong)time(NULL),clock(),startup->host_name);

		sockprintf(socket,"+OK Synchronet POP3 Server %s-%s Ready %s"
			,revision,PLATFORM_DESC,challenge);

		/* Requires USER command first */
		for(i=3;i;i--) {
			if(!sockgetrsp(socket,NULL,buf,sizeof(buf)))
				break;
			if(!strnicmp(buf,"USER ",5))
				break;
			if(!strnicmp(buf,"APOP ",5)) {
				apop=TRUE;
				break;
			}
			sockprintf(socket,"-ERR USER or APOP command expected");
		}
		if(!i || buf[0]==0)	/* no USER or APOP command received */
			break;

		p=buf+5;
		SKIP_WHITESPACE(p);
		if(apop) {
			if((response=strrchr(p,' '))!=NULL)
				*(response++)=0;
			else
				response=p;
		}
		SAFECOPY(username,p);
		if(!apop) {
			sockprintf(socket,"+OK");
			if(!sockgetrsp(socket,"PASS ",buf,sizeof(buf))) {
				sockprintf(socket,"-ERR PASS command expected");
				break;
			}
			p=buf+5;
			SKIP_WHITESPACE(p);
			SAFECOPY(password,p);
		}
		user.number=matchuser(&scfg,username,FALSE /*sysop_alias*/);
		if(!user.number) {
			if(scfg.sys_misc&SM_ECHO_PW)
				lprintf(LOG_WARNING,"%04d !POP3 UNKNOWN USER: %s (password: %s)"
					,socket, username, password);
			else
				lprintf(LOG_WARNING,"%04d !POP3 UNKNOWN USER: %s"
					,socket, username);
			sockprintf(socket,pop_err);
			break;
		}
		if((i=getuserdat(&scfg, &user))!=0) {
			lprintf(LOG_ERR,"%04d !POP3 ERROR %d getting data on user (%s)"
				,socket, i, username);
			sockprintf(socket, pop_err);
			break;
		}
		if(user.misc&(DELETED|INACTIVE)) {
			lprintf(LOG_WARNING,"%04d !POP3 DELETED or INACTIVE user #%u (%s)"
				,socket, user.number, username);
			sockprintf(socket, pop_err);
			break;
		}
		if(apop) {
			strlwr(user.pass);	/* this is case-sensitive, so convert to lowercase */
			strcat(challenge,user.pass);
			MD5_calc(digest,challenge,strlen(challenge));
			MD5_hex(str,digest);
			if(strcmp(str,response)) {
				lprintf(LOG_WARNING,"%04d !POP3 %s FAILED APOP authentication"
					,socket,username);
#if 0
				lprintf(LOG_DEBUG,"%04d !POP3 digest data: %s",socket,challenge);
				lprintf(LOG_DEBUG,"%04d !POP3 calc digest: %s",socket,str);
				lprintf(LOG_DEBUG,"%04d !POP3 resp digest: %s",socket,response);
#endif
				sockprintf(socket,pop_err);
				break;
			}
		} else if(stricmp(password,user.pass)) {
			if(scfg.sys_misc&SM_ECHO_PW)
				lprintf(LOG_WARNING,"%04d !POP3 FAILED Password attempt for user %s: '%s' expected '%s'"
					,socket, username, password, user.pass);
			else
				lprintf(LOG_WARNING,"%04d !POP3 FAILED Password attempt for user %s"
					,socket, username);
			sockprintf(socket, pop_err);
			break;
		}
		putuserrec(&scfg,user.number,U_COMP,LEN_COMP,host_name);
		putuserrec(&scfg,user.number,U_NOTE,LEN_NOTE,host_ip);

		/* Update client display */
		client.user=user.alias;
		client_on(socket,&client,TRUE /* update */);

		if(startup->options&MAIL_OPT_DEBUG_POP3)		
			lprintf(LOG_INFO,"%04d POP3 %s logged in %s", socket, user.alias, apop ? "via APOP":"");
		SAFEPRINTF(str,"POP3: %s",user.alias);
		status(str);

		sprintf(smb.file,"%smail",scfg.data_dir);
		if(smb_islocked(&smb)) {
			lprintf(LOG_WARNING,"%04d !POP3 MAIL BASE LOCKED: %s",socket,smb.last_error);
			sockprintf(socket,"-ERR database locked, try again later");
			break;
		}
		smb.retry_time=scfg.smb_retry_time;
		smb.subnum=INVALID_SUB;
		if((i=smb_open(&smb))!=SMB_SUCCESS) {
			lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) opening %s",socket,i,smb.last_error,smb.file);
			sockprintf(socket,"-ERR %d opening %s",i,smb.file);
			break;
		}

		mail=loadmail(&smb,&msgs,user.number,MAIL_YOUR,0);

		for(l=bytes=0;l<msgs;l++) {
			msg.hdr.number=mail[l].number;
			if((i=smb_getmsgidx(&smb,&msg))!=SMB_SUCCESS) {
				lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message index"
					,socket, i, smb.last_error);
				break;
			}
			if((i=smb_lockmsghdr(&smb,&msg))!=SMB_SUCCESS) {
				lprintf(LOG_WARNING,"%04d !POP3 ERROR %d (%s) locking message header #%lu"
					,socket, i, smb.last_error, msg.hdr.number);
				break; 
			}
			i=smb_getmsghdr(&smb,&msg);
			smb_unlockmsghdr(&smb,&msg);
			if(i!=0) {
				lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message header #%lu"
					,socket, i, smb.last_error, msg.hdr.number);
				break;
			}
			bytes+=smb_getmsgtxtlen(&msg);
			smb_freemsgmem(&msg);
		}

		if(l<msgs) {
			sockprintf(socket,"-ERR message #%d: %d (%s)"
				,mail[l].number,i,smb.last_error);
			break;
		}

		sockprintf(socket,"+OK %lu messages (%lu bytes)",msgs,bytes);

		while(1) {	/* TRANSACTION STATE */
			rd = sockreadline(socket, buf, sizeof(buf));
			if(rd<0) 
				break;
			truncsp(buf);
			if(startup->options&MAIL_OPT_DEBUG_POP3)
				lprintf(LOG_DEBUG,"%04d POP3 RX: %s", socket, buf);
			if(!stricmp(buf, "NOOP")) {
				sockprintf(socket,"+OK");
				continue;
			}
			if(!stricmp(buf, "QUIT")) {
				sockprintf(socket,"+OK");
				break;
			}
			if(!stricmp(buf, "STAT")) {
				sockprintf(socket,"+OK %lu %lu",msgs,bytes);
				continue;
			}
			if(!stricmp(buf, "RSET")) {
				for(l=0;l<msgs;l++) {
					msg.hdr.number=mail[l].number;
					if((i=smb_getmsgidx(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message index"
							,socket, i, smb.last_error);
						break;
					}
					if((i=smb_lockmsghdr(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_WARNING,"%04d !POP3 ERROR %d (%s) locking message header #%lu"
							,socket, i, smb.last_error, msg.hdr.number);
						break; 
					}
					if((i=smb_getmsghdr(&smb,&msg))!=SMB_SUCCESS) {
						smb_unlockmsghdr(&smb,&msg);
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message header #%lu"
							,socket, i, smb.last_error, msg.hdr.number);
						break;
					}
					msg.hdr.attr=mail[l].attr;
					msg.idx.attr=msg.hdr.attr;
					if((i=smb_putmsg(&smb,&msg))!=SMB_SUCCESS)
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) updating message index"
							,socket, i, smb.last_error);
					smb_unlockmsghdr(&smb,&msg);
					smb_freemsgmem(&msg);
				}
				if(l<msgs)
					sockprintf(socket,"-ERR %d messages reset (ERROR: %d)",l,i);
				else
					sockprintf(socket,"+OK %lu messages (%lu bytes)",msgs,bytes);
				continue;
			}
			if(!strnicmp(buf, "LIST",4) || !strnicmp(buf,"UIDL",4)) {
				p=buf+4;
				SKIP_WHITESPACE(p);
				if(isdigit(*p)) {
					msgnum=atol(p);
					if(msgnum<1 || msgnum>msgs) {
						lprintf(LOG_WARNING,"%04d !POP3 INVALID message #%ld"
							,socket, msgnum);
						sockprintf(socket,"-ERR no such message");
						continue;
					}
					msg.hdr.number=mail[msgnum-1].number;
					if((i=smb_getmsgidx(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message index"
							,socket, i, smb.last_error);
						sockprintf(socket,"-ERR %d getting message index",i);
						break;
					}
					if(msg.idx.attr&MSG_DELETE) {
						lprintf(LOG_WARNING,"%04d !POP3 ATTEMPT to list DELETED message"
							,socket);
						sockprintf(socket,"-ERR message deleted");
						continue;
					}
					if((i=smb_lockmsghdr(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_WARNING,"%04d !POP3 ERROR %d (%s) locking message header #%lu"
							,socket, i, smb.last_error, msg.hdr.number);
						sockprintf(socket,"-ERR %d locking message header",i);
						continue; 
					}
					i=smb_getmsghdr(&smb,&msg);
					smb_unlockmsghdr(&smb,&msg);
					if(i!=0) {
						smb_freemsgmem(&msg);
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message header #%lu"
							,socket, i, smb.last_error, msg.hdr.number);
						sockprintf(socket,"-ERR %d getting message header",i);
						continue;
					}
					if(!strnicmp(buf, "LIST",4)) {
						sockprintf(socket,"+OK %lu %lu",msgnum,smb_getmsgtxtlen(&msg));
					} else /* UIDL */
						sockprintf(socket,"+OK %lu %lu",msgnum,msg.hdr.number);

					smb_freemsgmem(&msg);
					continue;
				}
				/* List ALL messages */
				sockprintf(socket,"+OK %lu messages (%lu bytes)",msgs,bytes);
				for(l=0;l<msgs;l++) {
					msg.hdr.number=mail[l].number;
					if((i=smb_getmsgidx(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_ERR,"%04d !POP3 ERROR %d (%s) getting message index"
							,socket, i, smb.last_error);
						break;
					}
					if(msg.idx.attr&MSG_DELETE) 
						continue;
					if((i=smb_lockmsghdr(&smb,&msg))!=SMB_SUCCESS) {
						lprintf(LOG_WARNING,"%04d !POP3 ERROR %d (%s) locking message header #%lu"
							,socket, i, smb.last_error, msg.hdr.number);
						break; 
					}
					i=smb_getmsghdr(&smb,&msg);
					smb_unlockmsghdr(&smb,&msg);
					if(i!=0) {