Using Mail::CheckUser I would expect it to make an address as bad if an SMTP lookup fails. This is not happening:

Code snippet:

#timeout on DNS and SMTP network checks
$Mail::CheckUser::Timeout = 10;
$Mail::CheckUser::Treat_Timeout_As_Fail = 1;

foreach $add (@adds){ 
    
    $pm->start and next;

    if (Mail::CheckUser::check_email($add)){
        writeaddr(*GOODADDR, $add); #address is good
        print $add." good ".Mail::CheckUser::last_check()->{reason}."\
+n";
        $pm->finish;
    }else{  
        writeaddr(*BADADDR, $add); #address is bad
        print $add." bad".Mail::CheckUser::last_check()->{reason}."\n"
+;
        $pm->finish;
    }
}
$pm->wait_all_children;
[download]

Output:

$validemail mails 
janedoe@epatra.com good Cannot connect SMTP servers: 65.182.162.90
joeblow@attcanada.com good Cannot connect SMTP servers: 216.21.229.196

validemail is finished
[download]