Manual:$wgEnableUserEmail

Email settings: $wgEnableUserEmail
Set to true to enable user-to-user email.
Introduced in version:1.4.0
Removed in version:still in use
Allowed values:(boolean)
Default value:true (1.5+)
false (1.4)

DetailsEdit

Set to true to enable user-to-user email via Special:Emailuser. This can potentially be abused, as it's hard to track. This setting can be used to check if SMTP is set up correctly on your wiki.

Requires $wgEnableEmail to be true as well.

See alsoEdit