Manual:$wgRateLimits

Details
This setting provides a simple rate limiter to brake floods of edits and other potentially destructive behavior, like sending out emails to other users. It sets a maximum number of actions allowed in the given number of seconds; after that, the violating client receives HTTP 500 error pages until the period elapses. To check if a rate limit has been exceeded, use the User::pingLimiter function.

For example, to set a maximum of 4 edits per 60 seconds for "newbie" (i.e. non-autoconfirmed) users, add the following:

Version differences

 * The 'mailpassword' array was added in MediaWiki 1.7.0.
 * The 'emailuser' array was added in MediaWiki 1.10.0.