postfix: limit message rate

smtpd_client_message_rate_limit (default: 0)

The maximal number of message delivery requests that any client is allowed to make to this service per time unit, regardless of whether or not Postfix actually accepts those messages. The time unit is specified with the anvil_rate_time_unit configuration parameter.

By default, a client can send as many message delivery requests per time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_message_rate_limit = 1000

And see: http://www.postfix.org/anvil.8.html