diff --git a/actions/emailsettings.php b/actions/emailsettings.php
index 6eff06c0d6..67b991cdc8 100644
--- a/actions/emailsettings.php
+++ b/actions/emailsettings.php
@@ -326,7 +326,7 @@ class EmailsettingsAction extends AccountSettingsAction
             $this->showForm(_('Cannot normalize that email address'));
             return;
         }
-        if (!Validate::email($email, true)) {
+        if (!Validate::email($email, common_config('email', 'check_domain'))) {
             $this->showForm(_('Not a valid email address'));
             return;
         } else if ($user->email == $email) {
diff --git a/actions/invite.php b/actions/invite.php
index 788130c582..3015202e9e 100644
--- a/actions/invite.php
+++ b/actions/invite.php
@@ -68,7 +68,7 @@ class InviteAction extends CurrentUserDesignAction
 
         foreach ($addresses as $email) {
             $email = trim($email);
-            if (!Validate::email($email, true)) {
+            if (!Validate::email($email, common_config('email', 'check_domain'))) {
                 $this->showForm(sprintf(_('Invalid email address: %s'), $email));
                 return;
             }
diff --git a/actions/register.php b/actions/register.php
index 100ab74242..a6c1a903aa 100644
--- a/actions/register.php
+++ b/actions/register.php
@@ -191,7 +191,7 @@ class RegisterAction extends Action
             if (!$this->boolean('license')) {
                 $this->showForm(_('You can\'t register if you don\'t '.
                                   'agree to the license.'));
-            } else if ($email && !Validate::email($email, true)) {
+            } else if ($email && !Validate::email($email, common_config('email', 'check_domain'))) {
                 $this->showForm(_('Not a valid email address.'));
             } else if (!Validate::string($nickname, array('min_length' => 1,
                                                           'max_length' => 64,
diff --git a/config.php.sample b/config.php.sample
index 997c9d6b0b..9fccb84f3b 100644
--- a/config.php.sample
+++ b/config.php.sample
@@ -104,6 +104,10 @@ $config['sphinx']['port'] = 3312;
 // $config['site']['timezone'] = 'Pacific/Auckland';
 // $config['site']['language'] = 'en_NZ';
 
+// When validating user supplied email addresses, validate if the domain
+// is running an SMTP server.
+// $config['mail']['check_domain'] = true;
+
 // Email info, used for all outbound email
 // $config['mail']['notifyfrom'] = 'microblog@example.net';
 // $config['mail']['domain'] = 'microblog.example.net';
diff --git a/lib/default.php b/lib/default.php
index 30e43eefbd..9f64cc9e48 100644
--- a/lib/default.php
+++ b/lib/default.php
@@ -84,7 +84,8 @@ $default =
               'image' => 'http://i.creativecommons.org/l/by/3.0/80x15.png'),
         'mail' =>
         array('backend' => 'mail',
-              'params' => null),
+              'params' => null,
+              'domain_check' => true),
         'nickname' =>
         array('blacklist' => array(),
               'featured' => array()),
diff --git a/plugins/OpenID/finishopenidlogin.php b/plugins/OpenID/finishopenidlogin.php
index 50a9c15c87..ff0b451d30 100644
--- a/plugins/OpenID/finishopenidlogin.php
+++ b/plugins/OpenID/finishopenidlogin.php
@@ -265,7 +265,7 @@ class FinishopenidloginAction extends Action
             $fullname = '';
         }
 
-        if (!empty($sreg['email']) && Validate::email($sreg['email'], true)) {
+        if (!empty($sreg['email']) && Validate::email($sreg['email'], common_config('email', 'check_domain'))) {
             $email = $sreg['email'];
         } else {
             $email = '';
diff --git a/plugins/OpenID/openid.php b/plugins/OpenID/openid.php
index 0944117c00..b76497c28a 100644
--- a/plugins/OpenID/openid.php
+++ b/plugins/OpenID/openid.php
@@ -241,7 +241,7 @@ function oid_update_user(&$user, &$sreg)
 
     $orig_user = clone($user);
 
-    if ($sreg['email'] && Validate::email($sreg['email'], true)) {
+    if ($sreg['email'] && Validate::email($sreg['email'], common_config('email', 'check_domain'))) {
         $user->email = $sreg['email'];
     }