How can I disable all outgoing emails from a site all at once? There are some automated outgoing emails from my Drupal site like by core system mail, ubercart, webform and Rules. 

The reason is that I also have a test site which is exactly the copy of the production site. And I would like to disable all the outgoing emails so that no mails will be sent from the testing one by mistake.

I have installed "phpmailer" "mime mail" "mail editor" modules.

Is there an out-of-box way to do this?
The Maillog module is for exactly this purpose, as


  Maillog provides an easy possibility to log all Mails for debugging purposes. It's possible to prevent the mails to being sent, so there is no need for an extra mail server to test the mail functionality of other modules or the drupal core.