#!/usr/bin/perl
# Murty's Mail Daemon  version 1.0
# (c) Murty Rompalli    9/30/2001
# All rights reserved

use Socket ;
$| = 1 ;

######### Define User Variables

$port = 25 ;
$host = 'HOSTNAME' ;

$iport = 26 ;
$ihost = 'localhost' ;

$filter = 'filter.txt' ;
$log = 'log' ;
$uid = $gid = 99 ;     # This program runs as nobody:nobody

######### End of User Variables. Do not modify below this line.

$host .= ' mmail' ;
$paddr   = sockaddr_in($iport, inet_aton($ihost));
$proto = getprotobyname('tcp') || 6 ;
$SIG{CHLD} = 'IGNORE' ;
$SIG{INT} = \&CLOSE ;

-f $filter or die "$filter: No such file" ;
-r $filter or die "$filter: Cannot read" ;
-f $log or die "Error: $log must exist and be writable by $uid:$gid" ;

&startserver ;

for ($client = 'aaaa'; accept($client,Server) ; close $client++) {
     &handle unless fork ;
}

## End of Main

sub interact {

print "220 $host SMTP Ready\r\n" ;

while ($x = <$client>) {

if ($error > 4) {
   print "550 Too many errors\r\n" ;
   return 1 ;
}

if ($data) {
   undef $data if ($x eq ".\r\n" || $x eq "." || $x eq ".\n") ;
   my $result = &processdata($x) ;
 if($result != '') {
   if($result =~ /^5/) {
      print "550 Error occurred.\r\n" ;
      return 1 ;
   }
   else {
      print "250 Message Accepted.\r\n" ;
   }
 }
}
else {
   chomp $x ; if($x =~ /\r$/) { chop $x ; }
   if ($x =~ /^HELO\s+(.+)/i) {
          if($helo) {
             $error++ ;
             print "503 You already Said HELO\r\n" ;
          }
          else {
             $helo = $1 ;
             my $result = &processhelo($helo) ;
             if($result !~ /^5/) {
                  print "250 Hi There\r\n" ;
             }
             else {
                  print "550 Connection Denied\r\n" ;
                  return 1 ;
             }
          }
   }
   elsif ($x =~ /^MAIL\s+FROM:\s*(.+@.+)/i) {
         if($helo) {
              if($mail) {
                  $error++ ;
                  print "503 You already Said MAIL\r\n" ;
              }
              else {
                  $mail = $1 ;
                  my $mailraw = $mail ;
                  if($mail =~ /</ && $mail =~ />/) {
                      ($mail) = $mail =~ /<(.+)>/ ;
                  }
                  $mail =~ s/\s*//g ;
                  my $result = &processfrom($mailraw) ;
                  if($result !~ /^5/) {
                     print "250 Sender appears Ok\r\n" ;
                  }
                  else {
                     $error++ ;
                     print "550 Sender Blocked\r\n" ;
                     return 1 ; 
                  } 
              }
         }
         else {
              $error++ ;
              print "503 Say Helo First\r\n" ;
         }
   }
   elsif ($x =~ /^RCPT\s+TO:\s*(.+@.+)/i) {
         if ($helo && $mail) {
             my $toad = $1 ;
             my $toadraw = $toad ;
             if($toad =~ /</ && $toad =~ />/) {
                 ($toad) = $toad =~ /<(.+)>/ ;
             }
             $toad =~ s/\s*//g ;

             my $result = &processto($mail,$toad,$toadraw) ;

             if($result !~ /^5/) {
                 @to = (@to,$toadraw) ;
                 print "250 Recipient appears Ok\r\n" ;
             }
             elsif($result eq '5xx') {
              print "503 Type Email Address in Netscape/Internet Explorer\r\n" ;
             }
             else {
                 $error++ ;
                 print "550 Recipient Blocked\r\n" ;
             }
         }
         else {
             $error++ ;
             print "503 You forgot either HELO or MAIL\r\n" ;
         }
   }
   elsif ($x =~ /^DATA/i) {
         if($helo && $mail && @to) {
              my $datacmd = &processdatacmd($x) ;
              if($datacmd =~ /^5/) {
                  print "550 Data not acceptable\r\n" ;
                  $error++ ;
              }
              else {
                  $data = 1 ;
                  print "354 Proceed. End with a . on a line by itself\r\n" ;
              }
         }
         else {
              $error++ ;
              print "503 You didn't give all of HELO/MAIL/RCPT\r\n" ;
         }
   }
   elsif ($x =~ /QUIT/i || $x =~ /BYE/i) {
         print "221 Keep in touch\r\n" ;
         return 1 ;
   }  
   elsif ($x =~ /RSET/i || $x =~ /RESET/i) {
         undef $helo ; 
         undef $mail ; 
         undef $data ; 
         undef @to ;
         print "250 Reset Done\r\n" ;
   }
   else {
         $error++ ;
         print "500 Unknown Command\r\n" ;
   }
}   
}
}


sub connectsmtp {
socket(SOCK, PF_INET, SOCK_STREAM, $proto)  || die "socket: $!";
connect(SOCK, $paddr)  || die "Error: connecting to $ihost:$iport" ;
select SOCK ;
$| = 1 ;
return <SOCK> ;
}

sub closesmtp {
print SOCK "QUIT\r\n" ;
}

sub startserver {
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!"  ;
setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, 1) || die "setsockopt: $!" ;
bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!" ;
listen(Server,SOMAXCONN) || die "listen: $!" ;

($>,$))=($uid,$gid);
($<,$()=($uid,$gid);
}

sub CLOSE {
close Server ;
close $client;
close FH ;
&closesmtp ;
close SOCK ;
# $SIG{INT} = \&CLOSE ;
die 'Exiting on INT';
}

sub handle {
&openlog ;
my $connect = &connectsmtp ; 

select $client ; 
$| = 1 ;

if($connect !~ /^2/) {
  print "550 Connection Refused\r\n" ;
}
else {
  &interact ;
}

&closesmtp ;
close SOCK ;
close $client  ;
&closelog ;
exit ;
}

sub processhelo {
print SOCK "HELO ", $_[0], "\r\n" ;
return <SOCK> ;
}

sub processfrom {
print SOCK "MAIL FROM:", $_[0], "\r\n" ;
return <SOCK> ;
}

sub processto {
my ($sen,$rec,$recipient) = @_ ;
my $result = &filter($sen,$rec) ;

if ($result == 1) {
    print SOCK "RCPT TO:", $recipient, "\r\n" ;
    return <SOCK> ;
}
else {
    return '5xx' ;
}
}

sub filter {
my ($sen,$rec) = @_ ;
my ($sendom) = $sen =~ /.+(@.+)/ ; 
my ($recdom) = $rec =~ /.+(@.+)/ ;
my ($dline,$uline) ;
my ($allowed,$dneg,$uneg) = (1,0,0) ;

open(FH,"<$filter") or die "Error: opening filter" ;

while(<FH>) { 
   my $j = $_ ;
   next unless ($j =~ /^-/ || $j =~ /^\w/ || $j =~ /^@/) ;
   if ($j =~ /^$recdom/i) {
        $dline = $j ;
        last if ($uline) ;
   }
   elsif ($j =~ /^-$recdom/i) {
        $j =~ s/^-// ;
        $dline = $j ;
        $dneg = 1 ;
        last if ($uline) ;
   }
   elsif ($j =~ /^$rec/i) {
        $uline = $j ;
        last if ($dline) ;
   }
   elsif ($j =~ /^-$rec/i) {
        $j =~ s/^-// ;
        $uline = $j ;
        $uneg = 1 ;
        last if ($dline) ;
   }
} 

close FH ;

if ($dline) {
    $dline .= ' ' ;
    if ($dline =~ /\s$sen\s/i || $dline =~ /\s$sendom\s/i) {
       if ($dneg) {
         $allowed = -1 ;
       }
       else {
         $allowed = 1 ;
       }
    }
}

if ($uline) {
    $uline .= ' ' ;
    if ($uline =~ /\s$sen\s/i || $uline =~ /\s$sendom\s/i) {
       if ($dneg) {
         $allowed = -1 ;
       }
       else {
         $allowed = 1 ;
       }
    }
}

return $allowed ;
}

sub processdata {
#print SOCK $_[0], "\r\n" ;
print SOCK $_[0] ;
($data) ? return '' : return <SOCK> ;
}

sub processdatacmd {
print SOCK $_[0],"\r\n" ;
return <SOCK> ;
}

sub printlog {
print LOG join(' ',@_),"\n" ;
}

sub openlog {
open(LOG,">>$log") || die "Error: writing to logfile $log" ;
select LOG ;
$| = 1 ;
}

sub closelog {
close LOG || die "Error: closing logfile $log" ;
}