Brion wrote

E-mail functions are not always available on a given server (or may be available but non-functional), and in general open e-mail can be abused. Being able to disable all e-mail functions on the wiki prevents false presentation of unusable features, and disabling of user-to-user e-mail could cut down on abuse (for instance as a spam relay).

To summarise: As written on the IRC, we have now ( Brion_and_Tom together ) the following variables in DefaultSettings.php (1) $wgEnableMail (2) $wgEnableEmailUser (3) $wgEmailnotificationForUserTalkPages (4) $wgEmailnotificationForAllPages (5) $wgEmailnotificationForMinorChanges

The switches 1 to 2 are general switches, the switches 3 to 5 are used to determine the behaviour for the Email Notification for Page Changes, this patch scheduled for publication on 30.11.2004 See http://bugzilla.wikipedia.org/show_bug.cgi?id=454 and http://meta.wikipedia.org/Enotif