app/code/core/Mage/Customer/controllers/AccountController.php
00192     public function createPostAction()
{
00241                 if (true === $validationResult) {
00242                     $customer->save();


00243                     // Do your custom Code here to match the domains you want to make Confirmation Required for them.
                           $patterns = array('@foo.com','@boo.com','@bar.com');
                           $patterns_flattened = implode('|', $patterns);
                           if ( preg_match('/'. $patterns_flattened .'/i', $customer->getEmail(), $matches) )
                           { $customer->setIsConfirmationRequired(true);
                           }



00244                     if ($customer->isConfirmationRequired()) {
00245                         $customer->sendNewAccountEmail('confirmation', $this->_getSession()->getBeforeAuthUrl());
00246                         $this->_getSession()->addSuccess($this->__('Account confirmation is required. Please, check your e-mail for confirmation link. To resend confirmation email please <a href="%s">click here</a>.',
00247                             Mage::helper('customer')->getEmailConfirmationUrl($customer->getEmail())
00248                         ));
00249                         $this->_redirectSuccess(Mage::getUrl('*/*/index', array('_secure'=>true)));
00250                         return;
00251                     }
00252                     else {
00253                         $this->_getSession()->setCustomerAsLoggedIn($customer);
00254                         $url = $this->_welcomeCustomer($customer);
00255                         $this->_redirectSuccess($url);
00256                         return;
00257                     }