suggested change to post.php

One of my forums is currently still running punBB - but at some point I'd like to upgrade it to FluxBB.

I'm just trialling a small change to the code to try and stop some spammers from posting (we allow guest posting).

in post.php in my version of FluxBB approx line 160 I have

require FORUM_ROOT.'include/email.php';
 if (!is_valid_email($email))
    $errors[] = $lang_common['Invalid e-mail'];

is there any reason why this can't be added:

if(is_banned_email($email))
    $errors[] = $lang_common['Ban message'];