Manual:$wgRateLimits

Details
Simple rate limiter options to brake edit floods. 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.

e.g.  for a maximum of 4 hits in 60 seconds.

This option requires memcached. Also, note that it is experimental and likely to change.

Default value
Note that the 'mailpassword' array was added in MediaWiki 1.7.0.