If you don’t want to send lots of mail to your users when you’re testing your site, change the Devel module’s SMTP Library setting to “Log Only”. Then you can check your log to see all the mail that would’ve been sent. Handy!

To enable this only on your testing server, add the following to that domain’s settings.php:

$conf['smtp_library'] = drupal_get_filename('module', 'devel');