#!/usr/bin/perl
use Socket;

use warnings;
use strict;

my $port = 25;

my $sockaddr = 'S n a4 x8';
my $authcount=0;

my ($name, $aliases, $proto) = getprotobyname('tcp');
print "Port = $port\n";

my $thisaddr = gethostbyname('157.163.168.131');

my $this = pack($sockaddr, AF_INET, $port, $thisaddr);

socket(S, AF_INET, SOCK_STREAM, $proto);

bind(S,$this) || die "bind: $!";
listen(S,5) || die "connect: $!";

select(S); 
$| = 1; 
select(STDOUT);

my $pid;

for(;;) {
   print "Listening for connection....\n";

   my $mail_content = "";
   my $bool_data = 0;
   my $addr;
   ($addr = accept(NS,S)) || die $!;
    send(NS,"220 okey-dokey\r\n",0);
   my ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
   my @inetaddr = unpack('C4',$inetaddr);
   #print "$af $port @inetaddr\n";

   my $ctr=0;
   
   while (my $t=<NS>) {
      $ctr++;
      if( substr($t,0,4) eq "QUIT") {
         send(NS,"221 Bye\r\n",0);
         last;
      }
      print $t;
      #print FIL $t;
      if( substr($t,0,1) eq '.') {
         send(NS,"250 okey-dokey\r\n",0);
         $bool_data = 0;
         next;
      }
      if($bool_data){
        $mail_content .= $t;  
      }
      my $x=substr($t,0,4);
      if( ($x eq "EHLO") ||($x eq "HELO") || ($x eq "RCPT") || ($x eq "MAIL") ||
         ($x eq "RSET") || ($x eq "QUIT")) {
            send(NS,"250 " . $t . " okey-dokey\r\n",0);
      }
      if($x eq "DATA"){ send(NS,"354 End data with .\r\n",0); $bool_data = 1; }
   }
   close(NS);
   analyse_email($mail_content);  
}

sub analyse_email{
  my $mail = shift;
  print "\n\nEMAIL:\n".$mail;
}

 1:  > 220 mail.example.com SMTP Foo Mailserver
 2:  < HELO mail.example.org
 3:  > 250 Ok
 4:  < MAIL FROM: hans.muster@example.org
 5:  > 250 Ok
 6:  < RCPT TO: foo@example.com
 7:  > 250 Ok
 8:  < DATA
 9:  > 354 End data with .
10: < From: hans.muster@example.org
11: < To: foo@example.com
12: < Subject: Testmail
13: <
14: < Testmail
15: < .
16: > 250 Ok
17: < QUIT
18: > 221 Bye