use IPC::Open3 qw( );

open(my $mailer_fh, '|-', '/bin/mail', '-s', $hostn, $recipients)
   or die("Cannot execute mail command: $!\n");

open(my $msg_fh, '<', $disk_changes)
   or die("Cannot execute message file: $!\n");

print $mailer_fh $_ while <$msg_fh>;

close($mailer_fh)
   or die("Error sending mail message: $!\n");

$? == 0
   or die("Error sending mail message: $?\n");