Drush disable module updates email notifications
You can turn off just the email notify feature like this:

drush vdel update_notify_emails


(See in update.fetch.inc: $notify_list = variable_get('update_notify_emails', '');)

You might also want to consider the following alternative:

drush pm-disable update


This will completely disable the update module on your live server, which will also disable email notifications about Module updates.  At first blush, you might be sad that you won't be able to see the module updates page on your live server any more; however, you should really be doing your updating on a development machine anyway, so you can just re-enable update on the dev server.

To automatically re-enable the update module every time you sql-sync from live to dev, see symc_enable.drush.inc.

Finally, to insure that your dev machine does not send out unwanted email notifications, enable the devel module, and then add to your settings.php file:

$conf['mail_system'] = array(
  'default-system' =&gt; 'DevelMailLog',
);
$conf['devel_debug_mail_directory'] = '/path/to/dir/to/save/email';


Then, devel will intercept all email that is sent and write it into the target directory instead of emailing it.