Webmin and Virtualmin modules can provide functions to be run in the event a user is changed. This feature can be used by module developers to synchronize passwords in different locations, remove users from other services, or otherwise alter data about the user in other modules. If this option is disabled, other modules will not be notified, and additions, subtractions, and changes will not be replicated out to other modules. This option applies only to mailbox users, which are users that have mailbox/FTP/shell accounts within virtual domains.