Drupal 7 now has an option to use the site name (i.e. the value of the site_name variable) as the “Display Name” in the From header in system e-mails.
For example this would mean the sender might be “Acme Website” <email@example.com> as opposed to just the e-mail address alone.
In order to avoid disruption, this is not enabled by default for existing sites. New sites will have it enabled by default if they start from a new copy of default.settings.php
The feature can be enabled by setting the following variable to TRUE:
$conf['mail_display_name_site_name'] = TRUE;