It seems most developers I know have a story of running some sort of batch operation on a local Drupal site that triggers hundreds (or thousands!) of emails that are sent to the site's users, causing much frustration and ill will towards the site the developer is working on. One time, I accidentally re-sent over 9,000 private message emails during a test user migration because of an email being sent via a hook that was invoked during each message save. Filling a user's inbox is not a great way to make that user happy!
With Drupal, it's relatively easy to make sure emails are either rerouted or directed to temp files from local development environments (and any other environment where actual emails shouldn't be sent to end users). Drupal.org has a very thorough page, Managing Mail Handling for Development or Testing, which outlines many different ways you can handle email in non-production environments.
However, for most cases, I like to simply redirect all site emails to my own address, or route them to a figurative black hole.
Rerouting Emails to an Arbitrary Email Address
There's a simple module, Reroute Email, which allows you to have all emails sent through Drupal to be rerouted to a configured email address. This module is simple enough, but for even more simplicity, if you have a custom module, you can just invoke hook_mail_alter() to force all messages to a given email address. Example (assuming your module's name is 'custom' and you want to send emails to the configured 'site_mail' address):
<?php
/**
* Implements hook_mail_alter().
*/
function custom_mail_alter(&$message) {
// Re-route emails to admin when override_email variable is set.
if (variable_get('override_email', 0)) {
$message['to'] = variable_get('site_mail');
}
}
?>Now you can just add $conf['override_email'] = 1; to settings.php for any environment where you want all emails to be sent to the 'site_mail' configured email address. Pretty simple!
Directing emails to text files in /tmp
Another simple option, if you still don't want emails to be sent to the end user, but still want to see them in some form (in this case, a text file), is to enable the Devel module, then set your site's mail system to 'DevelMailLog' (like the following inside settings.php):
<?php
$conf['mail_system'] = array('default-system' => 'DevelMailLog');
?>Devel will now re-route all emails to .txt files inside your server's /tmp folder.
Comments
Just noting I wrote an alternative to the DevelMailLog that actually does a watchdog() on the mail so you can view them in the UI if you have dblog enabled. It's the HelperDebugMailLog available in https://drupal.org/project/helper
Is there a module you haven't written? :)
I've added information about the Helper module to https://drupal.org/node/201981.
I describe a way to accomplish the same thing here: http://checkmarkmedia.com/node/10 with the advantage that the changes are in the local development environment, and doesn't need to be configured in Drupal for every Drupal site. This is a safer approach, I think, since you don't have to remember to do it for each site.
That's a good approach for doing it for your own computer, but every developer on a team would still need to do the same thing; the advantage to using a configuration setting is that you can have a shared settings.php file (or use local.settings.php) that applies to all non-production environments, which disables or reroutes emails.