diff -urp email_verify_orig/email_verify.inc.php email_verify/email_verify.inc.php
--- email_verify_orig/email_verify.inc.php	2009-04-11 13:07:12.000000000 +0200
+++ email_verify/email_verify.inc.php	2011-02-16 17:39:34.924195001 +0100
@@ -21,6 +21,11 @@ function _email_verify_check($mail) {
 
   $host = substr(strchr($mail, '@'), 1);
 
+  // check if the email domain is not in blacklist
+  if (_email_domain_inblacklist($host)) {
+    return t('Email host %host is not permitted, please retry.', array('%host' => "$host"));	
+  }
+
   // Let's see if we can find anything about this host in the DNS
   if (!checkdnsrr($host, 'ANY')) {
     return t('Email host %host invalid, please retry.', array('%host' => "$host"));
@@ -108,3 +113,58 @@ function _email_verify_check($mail) {
   // Everything OK
   return;
 }
+
+function email_verify_blacklist() {
+  $form = array();
+	
+  $_blacklist = variable_get('hosts_blacklist',"gmail.com\nyahoo.com");
+  if(is_array($_blacklist)) {
+  	$blacklist = implode("\n",$_blacklist);
+  } else {
+  	$blacklist = $_blacklist;
+  }
+  
+  $form['hosts_blacklist'] = array(
+    '#title'   => t('Blacklisted Hosts'),
+    '#type'    => 'textarea',
+    '#required' => FALSE,
+    '#default_value' => $blacklist,
+    '#description' => t('Insert list of dns to blacklist'),
+  );  
+  
+   $form['submit'] = array(
+      '#type' => 'submit',
+      '#value' => t('Submit')
+    );
+  return $form;
+}
+
+function email_verify_blacklist_submit($form, &$form_state) {
+  
+  $blacklist = explode("\n",trim($form_state['values']['hosts_blacklist']));
+  
+  foreach ($blacklist as $key => $value) {
+  	if (is_null($value) || trim($value)=="" || !eregi("^[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", trim($value))) {
+      unset($blacklist[$key]);
+    }
+  } 
+    
+  variable_set('hosts_blacklist', $blacklist);
+    
+  drupal_set_message(t('Blacklist saved.'));
+}
+
+function _email_domain_inblacklist($host) {
+  
+  //blacklist array within not allowed dns
+  $blacklist = variable_get('hosts_blacklist',"");
+  if (is_array($blacklist)) {
+    foreach ($blacklist as $key => $value) {
+      if (trim($value) == $host) {
+        return true;
+      }
+    }
+  } else {
+    return false;
+  }
+}
diff -urp email_verify_orig/email_verify.module email_verify/email_verify.module
--- email_verify_orig/email_verify.module	2009-04-11 12:41:10.000000000 +0200
+++ email_verify/email_verify.module	2011-02-16 17:25:42.534195001 +0100
@@ -59,6 +59,15 @@ function email_verify_menu() {
     'type' => MENU_LOCAL_TASK, 
     'file' => 'email_verify.check.inc',
   );
+  $items['admin/user/user/blacklist'] = array(
+    'title' => 'Add a host in blacklist',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('email_verify_blacklist'),
+    'access arguments' => array('administer users'),
+    'type' => MENU_LOCAL_TASK, 
+    'file' => 'email_verify.inc.php',
+  );
+  
   return $items;
 }