Manual:$wgPasswordSender

Details
Password reminder email address The address we should use as sender when a user is requesting his password. Also used as the sender address for other email notifications.

Pre 1.17
Prior to 1.17 this setting was used as the literal string to use for the From: field in the e-mail, therefore anything that is valid in that field is allowed here.

The most common use-cases were:
 * E-mail address: "admin@example.com"
 * E-mail address with alternative display name: "Wiki Administrator "

1.17 onwards
As of 1.17, the From: field is constructed from this setting and $wgPasswordSenderName. Therefore this setting should contain just the e-mail address (as per the first example, above). If it is in any format then it will mangle the From: field. The second of the above examples can be achieved by using both settings, for example:

Usage in DefaultSettings.php
Note that from v1.5.0 upwards, the default value in DefaultSettings.php is initially set to the same value as was used in 1.4.x (with 'Wikipedia' changed to 'MediaWiki' in v1.6.0) but this is overridden later in DefaultSettings.php where it sets it to the value of $wgEmergencyContact, so this initial value is never seen (hence the current default value, above). This information is largely irrelevant, but is included here because it can cause confusion if you are browsing DefaultSettings.php to check the default value.