Manual:$wgEmergencyContact

Details
This allows the site administrator to specify an email address that the wiki can contact if something goes wrong. Current versions of MediaWiki (1.13 and above) do not use this setting, having delegated its uses to $wgPasswordSender, but future versions or extensions might.

Pre-1.13
This setting was very important before revision 38375. It was used for:
 * Certain error messages displayed to users
 * The return address for password reminders
 * The default sender address of email notifications to wiki members, such as page change notifications and watchlist notifications