my %users;

foreach my $line (<$file>) {
  my ($email, $ip) = parse_line($line);
  $users{$email}{$ip}++;
}

##</code><code>##

%users = (
          'joe@example.com' => {
                                 '192.168.10.24' => 2,
                                 '192.168.10.28' => 1
                               }
        );