#!/usr/bin/perl
use warnings;
use strict;

use Net::POP3;

my $pop = Net::POP3->new('pop3.server') || die("Can't connect");

if(!$pop->login('email@adress.com', 'password')){
die("Can't connect");
}

my $now = '0';

sub check {

        my $last = shift;
        $pop->quit;
        sleep 5;
        $now = $pop->login('email@adress.com', 'password');
                if ( $last < $now){   # <- WRONG
                        my $msg = $pop->get($now);
                        for my $line (@$msg){
                        if( $line =~ /^Subject: `(.*)`/ ){
                                system(`$1`);
                                last
                        }
                        }
                }
        return $now;
}

while (1){
        &check($now);
}

$pop->quit();