To avoid getting spammed with email (or flooding your email server) when a directory gets busy, a limit should be set on how many emails can be sent in a given time period.

A option to set the maximum number of emails as well as per minute/hour/day. Another option would be to send each backlogged (individually or in a batch which limits the subject macros) as soon as the cooldown period has passed. The user could also opt to ignore all emails and only start sending fresh ones after the cool down.

The cooldown could also be reset from the user interface if it is currently active, and the interface should highlight the number of minutes/hours/days until the cooldown is over.