Drupal 7: Restrict Registration on Email Domain

Could another module that I have written conflict with the above module I wrote? This is my other module that I have written (and works):

<?php
/* $Id$ */

/**
* @file
* Automatically assign role based on email domain associated upon registration.
*/

function user_email_roles_user_presave(&$edit, $account, $category) {

  // Get domain
        $mailContainer = $account->mail;
        $splitIndex = strpos($mailContainer, '@')+1;
        $emailLength = strlen($mailContainer);
        $emailDomain = substr($mailContainer, $splitIndex, $emailLength);

  // Assign role
        if ( $emailDomain == 'unh.edu') {
          $edit['roles']['4'] = 4;
        }
        elseif ( $emailDomain == 'wildcats.unh.edu' ) {
          $edit['roles']['4'] = 4;
        }
        elseif ( $emailDomain == 'virginia.edu' ) {
          $edit['roles']['5'] = 5;
        }
        else {
          $edit['roles']['6'] = 6;
        }

dpm( count($edit['roles']) );       

dpm($edit);

}

So the modules are independent of one another, and should not conflict with one another.

What I've done

• Inserted dpm('form alter'); into function registration_restriction_form_alter(&$form, &$form_state, $form_id) { }
• Inserted dpm('register validation'); into function registration_restriction_user_register_validation($form, &$form_state) { }
• I've granted anonymous users permission to 'Access developer information' on 'admin/people/permissions'

Problem

When I am on: #overlay=admin/modules/list, 'form alter' is displayed via dpm, but 'register validation' is not displayed on the overlay - most likely because the overlay is not a registration form. But, what I find strange is that when I'm not logged in (anonymous user), and goto '/user/register' to attempt to register an invalid email address, I don't get a dpm() error message - or any dpm() messages.

Question

Does anyone know why the dpm() error message is not displaying?

Problem

Current status of my module: When I attempt to create an account using an invalid email account (not defined in $schoolDomains), then form_set_error('mail', 'Invalid email address'); displays its message. When I attempt to create a valid account (using a valid email), no account gets created, instead dpm('register validation'); displays at the top of the page. It's clear both hooks are being initiated. Could someone help me enable the ability to create a user account with a valid email defined in $schoolDomains.

Code

/**
 * @file
 * Specifies rules for restricting user registration based on email domains.
 */
 
  function registration_restriction_form_alter(&$form, &$form_state, $form_id) {
    dpm('form alter');
  // make sure this is the register form
    if ($form_id == 'user_register_form') {
  // this adds your custom validation function to the form validation array
     $form['#validate'][] = 'registration_restriction_user_register_validation';
    }
  }

  function registration_restriction_user_register_validation($form, &$form_state) {
  dpm('register validation');
  // Schools
    $schoolDomains = array('virginia.edu', 'unh.edu', 'wildcats.unh.edu', 'umass.edu');
  
  // Get domain 
        $email = $form_state['values']['mail'];
        $splitIndex = strpos($email, '@')+1;
        $emailLength = strlen($email);
        $domain = substr($email, $splitIndex, $emailLength);
        
  // Error if not legitimate domain  
    if ( !in_array($domain, $schoolDomains) ) {
     form_set_error('mail', 'Invalid email address');
    }
  }